Wenger gave a prognosis of four to six weeks, meaning that Mustafi could return after the next worldwide break, but the Gunners boss will be keen to ensure that Mustafi is available for the Christmas period.
Summer signing Sead Kolasinac is a doubt for the weekend after picking up a hip problem while playing for Bosnia although Laurent Koscielny could play a part and he is set for a fitness test on Friday. "But he trained on his own and the first signs are positive so we made a decision to give him a test tomorrow".
"We lost Mustafi for about four to six weeks".
Wenger explained: "Koscielny has a definite final test tomorrow".
"Watford are a strong side, well balanced and a tough opposition for everybody".
"He didn't play in their first game and we lost him in the second - we have to cope with that now". I think about sorting out the problem, but overall I will decide completely tomorrow the line-up because Koscielny will have a test. "Now don't get me wrong, I don't run the most, we've got a lot of players that do that, but my numbers are good so I'm happy".
But Watford are yet to win any of their four home games in any competition this season, while Arsenal - 7/10 (1.70) to win the match outright - have won four on the spin ahead of their Saturday teatime trip to Vicarage Road, where they won 3-1 last season.
Alexis Sanchez will not report back from global duty with Chile until Friday, but Wenger has no concerns over the forward or Aaron Ramsey's mental state after their World Cup exits.
"The minor problem we have with Sead Kolasnic, we'll check him today, it's a hip problem", the Frenchman said on Thursday.