Mustafi was forced off in the first half of Germany's 5-1 FIFA World Cup qualifying victory over Azerbaijan on Monday (NZDT) and is not expected to return until after the next international break.
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.
Consequently, manager Arsene Wenger has concerns about how his defence will look for Saturday's Premier League trip to Watford.
"The minor problem we have with Sead Kolasnic, we'll check him today, it's a hip problem," Wenger said.
"We've lost Mustafi for about four to six weeks. I don't think he'll be available before the next international break.
"Koscielny has a definite final test tomorrow. At the moment, he's not available. He trained on his own and the first signs are positive.
"I have [concerns about the line-up]. I think about sorting out the problem, but overall I will decide completely tomorrow the line-up because Koscielny will have a test. It looks like if he survives the test he is capable to play."
Arsenal is on a run of four consecutive wins in all competitions and have not lost since the 4-0 reverse to Liverpool in August.