"We've lost Mustafi for about four to six weeks", Wenger told reporters on Thursday.
The former suffered a muscle injury during Germany's 5-1 win over Azerbaijan and manager Joachim Low's assessment suggested that Mustafi could be facing a long spell on the sidelines with a possible ligament tear. He produced a display that Wenger described as "outstanding" in a 4-2 win, which has sparked speculation over whether he will be awarded a new contract.
Kolasinac only managed one half while in action for Bosnia-Herzegovina against Belgium due to a hip injury, while Koscielny is set for a late fitness test on an Achilles injury.
"I haven't seen everybody because some players are coming back today, some even tomorrow like Alexis Sanchez", Wenger said on Thursday, when questioned about injuries picked up during the worldwide break.
Man Utd vs Liverpool is just another game, nothing to prove - Mourinho
However, the towering Belgian faces will definitely miss Saturday's clash with Liverpool and possibly longer, depending on the results of a scan.
Koscielny, on the other hand, skipped the recent global break to recover from an Achilles injury that has been a long-standing issue for the France defender.
Our lack of defensive experience could well pose as a problem however, with Calum Chambers, Rob Holding, Nacho Monreal, Maitland-Niles, Sead Kolasinac and Mo Elneny our only available stars for the three central roles and left-sided wing-back role.
"[Mesut] Ozil and [Danny] Welbeck are back in the group in normal training". "But he trained on his own and the first signs are positive so we made a decision to give him a test tomorrow".
"Koscielny has a definite final test tomorrow".