The global break is over Premier League is back with Arsenal set to travel across London to take on Watford on Saturday.
The news of Mustafi's injury may not be too much of a blow to Wenger though considering he hasn't featured for the Gunners so far this season.
Mustafi injured his thigh on global duty with Germany and it was not clear how long he would be sidelined for until manager Arsene Wenger confirmed today that it was approximately one month. "It looks like if he survives the test he is capable to play".More news: Wenger angers Arsenal fans after confirming Sanchez & Ozil could leave
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"Koscielny will have a final test tomorrow but at the moment he is not available". If he has no pain on his Achilles tendon he will play.
Wenger said forward Danny Welbeck (groin) and midfielder Mesut Ozil (knee) had recovered from their injures and were training, while defender Sead Kolasinac had a minor hip problem. I think about sorting out the problem, but overall I will decide completely tomorrow the line-up because Koscielny will have a test. "He trained on his own and the first signs are positive, so we chose to give him a test tomorrow".
Nacho Monreal is certain to keep his place at the back while Rob Holding is favourite to retain his position ahead of Per Mertesacker.
"Not all the players are back".
Wenger said contract talks with German worldwide Ozil, who is in the final year of his deal, were progressing well. "Mentally, I will have to assess the situation when he comes back tomorrow".