The Arsenal boss has admitted Sead Kolasinac is also struggling with a hip problem suffered playing for Bosnia.
And he is having to give Laurent Koscielny as long as possible to prove his fitness for Saturday's Premier League clash with Watford because he is so short of defenders.
With Calum Chambers also sidelined through injury it could mean Arsenal go into the Watford match without four senior defenders.
Wenger said: "I have concerns about my defence because of the injuries, and I need to think about that
"Kolasinac is a minor problem, a hip problem. We lost Mustafi for four to six weeks, I don’t think he will be available before the next international break.
"Koscielny will have a final test tomorrow but at the moment he is not available.
"He trained on his own and the signs were positive so we will test him on Friday.
"Watford are a strong side, well balanced and a tough opposition for everybody.