LONDON -- Arsenal centre-back Shkodran Mustafi has been ruled out until the next international break, while Laurent Koscielny faces a late fitness test ahead of Saturday's game at Watford.
Arsenal could face a defensive crisis if Koscielny is unable to play at Watford as it would leave Arsene Wenger without his two top centre-backs.
Mustafi suffered a muscle tear in his thigh while playing for Germany during the recent international break and Wenger said he will be out for at least four weeks.
"I don't think he'll be available before the next international break [in November]," Wenger said.
Koscielny, meanwhile, is still struggling with a flare-up of his chronic Achilles problem but could play on Saturday if he comes through a fitness test on Friday.
"Koscielny has a definite final test tomorrow. At the moment, he's not available," Wenger said. "He trained on his own and the first signs are positive, so we decided to give him a test tomorrow."
If Koscielny cannot play, Wenger could stick with a back three by playing Per Mertesacker and Rob Holding together with Nacho Monreal -- or he might be tempted to revert to a four-man defence.
The Arsenal boss said that the injuries could force him to make some tough decisions.
"I think about sorting out the problem, but overall I will completely decide what I do tomorrow because Koscielny will have a test then," he said. "He worked quite hard physically, he looks like he is capable of playing if he survives the test. If he has no pain on his Achilles tendon, he can play. I will decide that tomorrow."
Mesut Ozil and Danny Welbeck are both available again after recovering from injury problems, while Alexis Sanchez and Aaron Ramsey will be assessed after returning from a disappointing international break where Chile and Wales both missed out on the World Cup.
Wenger also addressed the possibility of Arsenal's Dec. 23 fixture against Liverpool being moved to Christmas Eve for TV purposes, saying that a late kickoff would be unacceptable on that date.
The proposal to move the game -- possibly to a 4 p.m. GMT kickoff -- has angered fans from both clubs, but especially Liverpool supporters who would struggle to travel back home on public transport that evening.
"I know that we have to adapt to the schedule dictated by the television, but overall I would say if that happens personally I think it should not be played after 2 p.m. latest on Christmas Eve," Wenger said. "I would say if we had to play we should not play after 2 p.m.
"Personally I would prefer to be at my home on Christmas night and celebrate Christmas, but I still feel that could happen if we played early on the day. What you wouldn't like to sacrifice is the evening with the family for people, but overall we go towards a society where religion isn't considered anymore in any decision and where people want as well to watch football in the Christmas period."