Mathieu Debuchy dislocated his right shoulder after crashing into the advertising boards during the first half of Arsenal’s 3-0 victory over Stoke City.
The France defender tangled with Stoke midfielder Marko Arnautovic after 11 minutes and was left clutching his upper arm having slammed into the path around the pitch and then the promotional boards.
He was treated on the sidelines for six minutes by the Arsenal medical staff before an x-ray in the treatment room at the Emirates confirmed the club’s worst fears.
Wenger said: "He has a dislocated shoulder. It is difficult (to say how long he will be out) – you need a diagnosis from a specialist. We don’t know yet, but he will certainly not play next week. Kieran Gibbs still has an inflamed ankle. Monreal and Debuchy can play centre-back, but if Gibbs is not here Monreal cannot play center-back and if Debuchy is not here he cannot play centre-back. This is a position where we are short."
Wenger also admitted Debuchy’s injury is likely to change his transfer plans for the month ahead.
Debuchy, who signed from Newcastle United in July, has already missed three months of the season following a serious ankle injury suffered against Manchester City in September.
Goalkeeper Wojciech Szczesny, meanwhile, had been left to watch on from the bench as Colombian David Ospina made his Premier League debut, the Poland international having found himself the center of some negative headlines earlier this week for smoking in the showers after the defeat at Southampton.
Wenger, however, stressed his decision was not based on any disciplinary action.
The Arsenal boss said: "I do not want to talk too much about that because the more I talk, the less I inform you. You know how you can take a decision (like that as a player). It was a decision for today’s game. Szczesny is our No 1 competing with Ospina and (Emiliano) Martinez – that is our job."