Obviously it will be a big boost for Arsenal to have the centre-back available for their crunch North London Derby but he's going to be sorely missed over the coming weeks.
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.
There is better injury news, however, regarding Sead Kolasinac, who was forced off whilst playing for Bosnia on Tuesday night with the left-sided defender expected to be available for the game against the Hornets.
GETTYArsene Wenger's Arsenal take on Watford on Saturday afternoon (5.30pm) Kolasinac is a minor problem, a hip problem. "But he trained on his own and the first signs are positive so we chose to give him a test tomorrow".
"Koscielny will have a final test tomorrow but at the moment he is not available".
Asked about Mustafi on Thursday, Wenger confirmed to the media: 'We have lost Mustafi for about four to six weeks.
"I will decide what I have to do when Koscielny has his test tomorrow".
"I didn't expect him to play and Germany had already qualified so their matches would have been less intense". We will check him today.
Wenger said: "We will assess Sanchez when he comes back, I watched the Brazil game and he got some special treatment in that game".