The Germany defender suffered the injury during his country's 5-1 victory over Azerbaijan on Sunday, pulling up and going to ground in the build-up to the visiting side's goal.
Whenever the German is available again, Arsenal manager Arsene Wenger has something of a defensive selection poser for the trip to Hertfordshire should he look to continue with a three-man backline.
The playmaker was rested by Germany during the global break, meaning Ozil could return to action against the Hornets, but faces a battle for a starting spot.More news: 2.5 million more consumers affected, ex-CEO faces Congress
"I didn't expect him to play and Germany had already qualified".
"I will decide what I have to do when Koscielny has his test tomorrow". He didn't play in the first game, and we lost him in the second game against Azerbaijan at home. "It looks like if he survives the test he is capable to play". "We have to cope with that now". At the moment, he's not available.
Sead Kolasniac, who has impressed so far this season at left-back, has come back from global duty with a minor hip problem too, which is being assessed today.
Watford have made an impressive start to the new league campaign, as they are now eighth in the standings, level on points with both Liverpool and Burnley, while they also won their last meeting with Arsenal, securing a 2-1 success at the Emirates Stadium in January. Wenger did however have good news regarding Mesut Ozil. "Mentally, I will have to assess the situation when he comes back tomorrow". He trained on his own and the first signs are positive.