Arsene Wenger says that he is unsure how long Laurent Koscielny will be sidelined for.
Koscielny limped out of Sunday’s 2-2 draw with Manchester City, the Frenchman substituted at half-time after injuring his Achilles heel.
Wenger says that the 31-year-old will undergo a scan on Tuesday to discover the extent of the knock.
The manager also confirmed that Alex Oxlade-Chamberlain and Aaron Ramsey are likely to return against West Ham on Wednesday.
“Oxlade-Chamberlain and Ramsey have a test today,” he said. “There is a good chance they are back in the squad.
“Apart from that we lose Koscielny. For how long? I don’t know.
“It is serious. It’s an Achilles problem. If he has ruptured some fibres then it could be a few weeks. If it’s just inflammation he could be back for the weekend.
“He will have a scan today and we’ll know more tomorrow.”
Wenger also ruled goalkeeper Petr Cech out of the West Ham clash, while declaring him doubtful for Monday’s meeting with Crystal Palace.
But the manager confirmed the return of captain Per Mertesacker, who has not featured all season.
He added: “Per Mertesacker is available to play. He could be in the squad for tomorrow.”