Wenger feared the worst over Wilshere injury

Arsene Wenger yesterday mapped out Jack Wilshere's long road to recovery, but admitted that even Wilshere's likely 22-week absence is shorter than the club had first feared. Arsenal, who host Olympiakos this evening, will probably be without their player of the season until next March.

Wilshere had surgery on Monday, which inserted a screw to repair a stress fracture in his right ankle, and Wenger admitted that the prognosis might have been much worse. "When people go into surgery you never know what they find," he said. "What they found was a very clean ankle and they came out very positive. Sometimes you are scared the player goes in and they say 'look, it was worse than what we expected'. Or they say 'it was better'. They said it was better than what they expected it to be."

The Arsenal manager detailed Wilshere's next few months. "He will be 12 weeks in a boot and after that it is rehab," he said. "Twelve weeks brings us to around Christmas. If all goes well, you would think he will be fit again to play in half the time you are in the boot – six weeks. Count 10 to be closer to the truth, so it's 22 weeks to be capable to play football again." Wenger was confident that there would be "no worries" concerning Wilshere's participation in the European Championships next summer.

Wilshere first felt the ankle injury in England's draw with Switzerland on 4 June. He played in pre-season for Arsenal, hoping that the injury had improved, and Wenger yesterday defended the club's response. "We made a scan before we left [for the pre-season Asia tour] and it was all right. This crack in the bone became worse and worse. People say to me it didn't heal because there is no blood supply so it doesn't glue together any more. We had to put a screw in. When you see the scan it looks like a little hole in the bone. We needed to screw that together because it would not heal."

With Arsenal badly hit by injuries, Wenger believes his squad is struggling to balance the twin demands of domestic and European competition. "We paid a heavy price in the Premiership for our performances in the Champions League," he said. "We played Liverpool after having played Udinese and we played Man United after having played at Udinese, a game that was terrible for us because it was 33 degrees at night, it was unbelievably hot. We had to give everything, we lost three or four players in that game and we had to go to Man United, it was a bit too much. And after we went to Dortmund, we went to Blackburn."

Arsenal will be without Gervinho, Laurent Koscielny and Theo Walcott this evening, all of whom have short-term injuries which will not necessarily keep them out of Sunday's north London derby. Andrei Arshavin is likely to start, and Wenger praised the Russian forward as "very conscientious" and a "hard worker in training". When asked whether he was as keen for Arshavin to sign a new deal as he was for Robin van Persie, Wenger said: "Robin is different, Andrei [30 years old] is older, Robin [28] is younger. Robin finishes at the age of 33, Andrei finishes at age of 33, I think."

Three key confrontations: Where tonight's match will be won or lost

Robin van Persie v Olof Mellberg

Van Persie will confront an old foe this evening, in former Aston Villa defender Olof Mellberg. The Swede enjoyed seven seasons at Villa Park, honing his rugged, assertive style. Van Persie will never beat Mellberg in the air, but will instead hope to drag him out of position.

Mikel Arteta v Pablo Orbaiz

Two Basque midfielders will battle for control this evening. Orbaiz, from Pamplona, played over 200 games for Athletic Bilbao, before leaving for Olympiakos on a season-long loan. He will tussle with Arteta, from San Sebastian, for possession and territory.

Bacary Sagna v Kevin Mirallas

Olympiakos' interchanging front three includes Kevin Mirallas, the young Belgian forward formerly of Lille and Saint Étienne. As Mirallas exchanges positions with Algerian pair Djamel Abdoun and Rafik Djebbour, Sagna must be careful that everyone is marked.