Arsene Wenger hit out at "useless" officiating in Arsenal's shock Champions League defeat in Braga where captain Cesc Fabregas suffered a fresh hamstring problem and Emmanuel Eboue was carried off with a knee injury.
The Gunners lost 2-0 in the stunning Estadio Municipal, carved out of a quarry, after a late double from Matheus, which leaves Arsenal yet to guarantee a place in the last 16 and set to finish runners-up to Shakhtar Donetsk.
Arsenal were denied a second-half penalty by Hungarian referee Viktor Kassai when substitute Carlos Vela was fouled by Alberto Rodriguez but was awarded a booking rather than a spot-kick.
And just minutes later the London side found themselves down to 10 men following a late challenge by Brazilian Matheus which left full-back Eboue facing a spell on the sidelines with medial ligament damage.
While Arsenal never really hit top gear, Wenger was less than impressed by the behaviour of a team the Gunners thrashed 6-0 on matchday one.
"Everybody is free to play the way they like, and they won. We could play 10 matches like that and win eight or nine times, but this was the one we didn't," Wenger lamented.
"It is difficult to understand how we did not get a penalty, and how Carlos Vela got a yellow card (for diving). It remains a complete mystery.
"We are going through a period where we have bad luck.
"We had Eboue kicked off the park without any punishment and we also had the penalty turned down.
"What was the fifth official doing? We have another proof that it is absolutely useless, this system.
"Then when we were 10 against 11, we made a mistake at the back, there was a minimum of communication and that's where we were punished."
Wenger made seven changes following the derby defeat to Tottenham at the weekend, but defended his team selection.
He said: "We had enough on the pitch to make a goal, but football is like that when the other team focuses not to play.
"They used every single trick in the book to slow the game down."
Wenger hopes Arsenal's injuries will not prove too bad.
"Eboue will be out for a while and we will have to assess Fabregas. It could be two to three weeks," he said.
"It is very disappointing because I had a hesitation to play him before the match started.
"I took the gamble and it backfired on us."
Arsenal must now beat Group H whipping boys Partizan Belgrade at home in a fortnight to make sure of a place in the knockout stages.
"It is hard to swallow, but now we have to win our last game," Wenger said.
"The most important thing for us now is to qualify."
Braga coach Domingos Paciencia, whose side are now level on points with Arsenal, refused to be drawn on Wenger's blast, saying: "I don't want to comment, because it is just the personal opinion of the Arsenal manager."Reuse content