Arsenal manager Arsene Wenger has admitted he is unsure how long defender Laurent Koscielny will be out for, after the France international injured his Achilles tendon against Manchester City.
Arsenal skipper Koscielny was forced off at half-time at the Emirates Stadium, and the Gunners boss revealed afterwards that the 31-year-old's layoff is yet to be determined.
"I don't know how long Koscielny will be out for," Wenger said after the 2-2 draw with City on Sunday, live on Sky Sports.
"He came off at half-time with an Achilles problem. How long will that last? I don't know."
Wenger and co host West Ham on Wednesday night, before successive Monday Night Football trips to Crystal Palace and Middlesbrough, both live on Sky Sports 1 HD.
Ahead of Wednesday's fixture, Wenger also revealed that he could welcome back a couple of faces from injury for West Ham after the "great mental resources" his side showed against Pep Guardiola's City.
"Ramsey and Oxlade-Chamberlain could feature on Wednesday," Wenger added.
"Overall, we started with quite a high level of anxiety. We were punished straight away, so it was a mental test. You could see that the team were touched on the confidence front and that the fluency in our game suffered.
"We have shown great mental resources because we went a goal down twice and once at the worst moment in a game - just before half-time. On top of that, we lost Koscielny at half-time."