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Dinamo Zagreb have revealed that their midfielder Arijan Ademi failed a doping test after the Croatian side's Champions League win over Arsenal last month.
Ademi played the full 90 minutes of Dinamo's 2-1 home victory in the Group F match on 16 September.
If the 24-year-old's B sample is also positive, the player could face a ban, but there are no rules to disqualify teams from the competition unless two or more players fail drug tests.
In a statement on their website, the club said that; "Due to a positive doping test after the Champions league match Dinamo - Arsenal, UEFA instigates disciplinary proceedings against Ademi."
Show all 22 1 /22Arsenal vs Manchester United player ratings Arsenal vs Manchester United player ratings PETR CECH: 6 out of 10 One of his quietest games in an Arsenal shirt, but when called upon he was up to the challenge. Never was this more the case than when he blocked a Martial strike from close range with his feet.
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Arsenal vs Manchester United player ratings HECTOR BELLERIN: 7 out of 10 Relished the opportunity to pit himself against an out of position Young, powering forward at every opportunity to add another body to the attacking thrust.
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Arsenal vs Manchester United player ratings PER MERTESACKER: 6 out of 10 Bar more than one brain freeze this was a very impressive display from the captain, who calmly moved the ball forward. He dealt well with crosses into the area but at times was guilty of overconfident dawdling in his own half.
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Arsenal vs Manchester United player ratings GABRIEL: 7 out of 10 Gabriel provided further evidence that Wenger has three very capable defenders in his squad, and three who compliment each other well. This was a tough-tackling display from the Brazilian, never giving Martial or Rooney a moment to settle.
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Arsenal vs Manchester United player ratings NACHO MONREAL: 7 out of 10 As reliable a performance as any on the Arsenal pitch, he won’t get the plaudits but not once did Monreal put a foot wrong. Or indeed a head as he dealt well with United’s aerial barrages. That allowed Alexis to unleash his gung-ho best with utter confidence.
Arsenal vs Manchester United player ratings SANTI CAZORLA: 7 out of 10 A brilliant opening 45 minutes saw him at the heart of Arsenal’s powerful running, finding his teammates with space ahead of them and tackling excellently. His two-footedness was vital in crafting Arsenal’s opportunities; United’s defenders had no idea where the ball was heading next.
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Arsenal vs Manchester United player ratings FRANCIS COQUELIN: 8 out of 10 Blew away any doubts of lingering injuries with an imposing display that saw him grab the midfield warzone and turn it into a rout. He slid in often, but he was always in control and invariably knew what he was doing. After his performances against City and United last season this is further proof he is a big game player.
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Arsenal vs Manchester United player ratings AARON RAMSEY: 7 out of 10 That this was his best performance this season says more for his slow start, but as he came further infield in deep positions he seemed far more capable. He still needs to rediscover his composure in front of goal, but he was a valuable component in an excellent performance.
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Arsenal vs Manchester United player ratings MESUT OZIL: 8 out of 10 A wonderful evisceration of United’s one-pace defence in the opening 10 minutes left his supporters in dreamland. And he kept it up. His ability to find space left the static United midfield dumbfounded, and he then provided excellent passes to his colleagues.
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Arsenal vs Manchester United player ratings ALEXIS SANCHEZ: 9 out of 10 A special player indeed who thoroughly deserved each of his goals. The confidence with which he ran at Darmian and Smalling was a sight to behold, and it never seemed to stop. On this sort of form, six goals in eight games, is there a better player in the league?
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Arsenal vs Manchester United player ratings THEO WALCOTT: 7 out of 10 May not have got the goal his play thoroughly deserved but his pace and direct running caused Blind and Smalling no little headache. Increasingly impressive is his ability with his back to goal, a part of his game that is clearly improving. A well-crafted assist for Ozil’s goal capped a good game indeed.
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Arsenal vs Manchester United player ratings DAVID DE GEA: 5 out of 10 Could do little about Arsenal’s first-half treble, having to sit back and watch his defence collapse before his very eyes. However he could have been more convincing on crosses considering the undersized Arsenal attack.
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Arsenal vs Manchester United player ratings ASHLEY YOUNG: 5 out of 10 Was left looking the naïve one by the direct running of Bellerin, though he would have doubtless appreciated some support from Memphis, and he struggled as much on the ball as off it. Bar one occasion when he shot from 25 yards out he offered nothing going forward.
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Arsenal vs Manchester United player ratings CHRIS SMALLING: 5 out of 10 As his colleagues collapsed around him he gave it his best shot to hold it all together, but it was just too much for a defender who gave the ball away much too often.
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Arsenal vs Manchester United player ratings DALEY BLIND: 5 out of 10 Walcott exposed his limitations as a centre-back. Stepping forward to intercept he looks composed but when players try to get behind him he does not know what to do.
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Arsenal vs Manchester United player ratings MATTEO DARMIAN: 4 out of 10 Was eviscerated by Sanchez, who took the ball past his opponent at will. When a defender considers his best option to be dragging his opponent to the floor, as Darmian did more than once, it’s clear something has gone badly wrong. It was little surprise that Van Gaal withdrew him at half time.
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Arsenal vs Manchester United player ratings MICHAEL CARRICK: 4 out of 10 Whether it was Carrick or Schweinsteiger that shiuld have missed out the decision not to play Schneiderlin was bizarre. He was simply overrun by players much quicker than him, though he was too nervy in possession as well.
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Arsenal vs Manchester United player ratings BASTIAN SCHWEINSTEIGER: 4 out of 10 His eagerness to press Coquelin and Cazorla left his defence with no shield, and the midfielder could scarcely lay a glove on either. Offered no protection whatsoever from the fast running Arsenal, too often arriving just in time to watch Arsenal go close or score.
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Arsenal vs Manchester United player ratings JUAN MATA: 5 out of 10 An anonymous display from a player capable of far, far better. Monreal could take the ball from the attacker at will, who on no occasion threatened to burst into life. More than once he gave the ball away under no pressure.
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Arsenal vs Manchester United player ratings WAYNE ROONEY: 5 out of 10 He usually relishes the opportunity to take on Arsenal, and he rarely shied away from the limelight. But this was one of those Rooney games where he runs around a lot, desperately trying to influence the game and ending up helping no-one.
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Arsenal vs Manchester United player ratings MEMPHIS DEPAY: 5 out of 10 Full of willingness in attack, he dropped deep and infield to try something, anything to drag United back into the contest. But then it was little wonder that Young found himself with no protection as Arsenal streamed forward, meaning he was a likely candidate for an early bath.
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Arsenal vs Manchester United player ratings ANTHONY MARTIAL: 7 out of 10 When something good happened for United you could be certain that the 19-year-old was involved. His raw pace gave Mertesacker in particular problems, and he showed outstanding technical skills to turn and volley and draw a great save out of Cech.
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The club said it was "surprised because Ademi was selected for doping control six times this year and results were negative every time, as well as results of every other player who was selected for doping control by UEFA or Croatian Anti-Doping Agency."
Though he played for Croatia at youth level, Ademi is a Macedonia international, winning four caps.
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