The Frenchman indicated Alex Song or Sebastien Squillaci will play in central defence and said Alex Oxlade-Chamberlain could keep his place in the team after his goal on Wednesday
The Belgian will miss Sunday’s clash against Tottenham Hotspur and will still not have recovered after the international break.
His absence will be a blow for Wenger, who indicated it was a straight shoot-out between Sebastien Squillaci or Alex Song, who played there against Olympiakos on Wednesday, for a spot in central defence.
“It will be a fraction longer than expected [before Vermaelen returns]. He will not be straight back after the international break. It will be one or two weeks later,” he told reporters.
“[Yossi] Benayoun and Squillaci are completely fit. Squillaci lacks match fitness, Benayoun does not.
“Squillaci will not be fit enough to start the game. If I am tempted [about playing Song in central defence] I can answer honestly 'yes'. Will I do it? Honestly I don't know yet.
“Koscielny looks to be definitely out for Sunday, it looks short for him. He couldn't absorb any test today.”
Arsenal also have a number of absentees up front, with Theo Walcott and Gervinho both racing against time to be fit for the Sunday’s clash.
But should they be unavailable, it could force Wenger to start Alex Oxlade-Chamberlain once again after the youngster found the back of the net in his last two outings for the Gunners.
“For Walcott and Gervinho a decision will be made on Saturday or Sunday. The most likely to be fit of the two looks to be Walcott.,” added Wenger.
And on Oxlade-Chamberlain he said: “He is a possibility to be in the squad, I haven't picked the team yet.
“When you are ready for the Champions League you are ready for the Premier League.
“People want to make stars overnight in modern football but it is not like that.
“What is very positive for me is that he has shown he has the talent to be a very good future player but that he also still has things to work on.
“I have big hopes for him as well but I do not want to be impatient.”