Wilshere faces weeks on sidelines as Arsenal also finally lose Nasri

Key midfielder's ankle injury adds to Gunners gloom ahead of tonight's crucial qualifier while City get their man

Arsene Wenger revealed yesterday that Jack Wilshere has been diagnosed with a long-term ankle problem that will rule him out of action until well into next month, on the day that Samir Nasri's transfer to Manchester City finally went through.

The Arsenal manager, whose team face Udinese in the second leg of their Champions League qualifier in Italy tonight, said that the 19-year-old had broken down in training on Monday with a recurrent problem that the club fear could develop into a stress fracture if he continues playing. It means that Wilshere will not play tonight or against Manchester United on Sunday and will not feature for England in their two Euro 2012 qualifiers next month.

There was some good news for Wenger yesterday: the Arsenal manager will be permitted to coach his side from the dugout tonight, with Uefa suspending his further two-match touchline ban while Arsenal's appeal is heard. However, the club were also told by the Football Association that, along with Newcastle United, they would be fined £30,000 for failing to control their players in their game 12 days ago.

Wenger said Wilshere first felt the problem with his ankle during the Euro 2012 qualifier for England against Switzerland in June. Wenger said: "Jack was always out long-term because he was out three weeks. He had a setback. It's a hot spot on the bone of his ankle that if you continue to play can lead to a stress fracture. So we had to stop him.

"During the holidays it was all right and then his pain increased when we were on tour in Asia. We had two good test days on Friday and Saturday. Monday morning, we had a test with the squad and he felt it again. There is no chance he will be fit for England. He's in a [protective] boot now. It's not ideal for us on the day we sell Nasri.

"Maybe it is a consequence of last season, he was in the red like I told you [when Arsenal convinced Wilshere to withdraw from the Under-21s European Championship] and, in fairness, what nobody wanted to hear. We knew he was in the red [physically] in the last two months and we continued to play him because we had no choice. But maybe it is a consequence of the overuse last year."

Although Nasri trained with his Arsenal team-mates in the morning, Wenger told him after the session that the club had reached agreement with City. Nasri travelled to Manchester for a medical. Nicklas Bendtner also missed the trip with an ankle injury and Henri Lansbury was left out of the squad. Wenger's squad to face United looks even more depleted, when the suspensions for Alex Song and Gervinho are taken into consideration, as well as injuries to Wilshere, Laurent Koscielny, Abou Diaby and Kieran Gibbs.

Having said earlier in the summer that if Arsenal were to sell both Fabregas and Nasri they could not consider themselves a big club, Wenger re-positioned himself yesterday to say that the two players' situations were very different – and that he had had no choice but to allow them both to leave.

Wenger said: "We did not want to lose Fabregas, but we were forced into a situation we didn't want. Nasri was a situation where the player didn't want to extend his contract with the proposals he had somewhere else. What kind of commitment can you have when the player is not there long-term? That is the question you have to answer.

"I don't question Samir Nasri's commitment or professionalism because he was in training [yesterday]. If I told him, 'You come with us and play', he would have played like he did on Saturday, but you wonder what kind of a commitment you can have. Football rules are made like that. A certain player can be worth a lot of money today and nothing in six months so it doesn't look completely logical, but we were forced into a decision like that for psychological and financial reasons."

Wenger played down the pressure around the tie, which Arsenal lead 1-0 from the first leg. "It's not critical," Wenger said, "it's for us an opportunity to qualify for the group stage of the Champions League, so it's a good opportunity."

Having negotiated deals of around £60m for Cesc Fabregas and Nasri this summer, Wenger will have a week to try to strengthen his squad. The targets such as Yann M'Vila, Eden Hazard and Marvin Martin are all expected to reserve judgement until tonight's result. Phil Jagielka, as the Everton manager, David Moyes, said last week, has not pushed for a move.