William Gallas is likely to miss Arsenal's trip to Charlton on Saturday.
The French defender was forced off in injury time against Porto on Tuesday after picking up a hamstring problem.
In his post-match press conference, his manager ruled him out of the weekend's match and suggested the injury may stretch into international week.
"Gallas has a hamstring problem," said Arsène Wenger. "It looked to me very serious. We hope it's not too bad, but for Saturday certainly he'll be short. [After that] I don't know, if he will be available for the French national team or not."
Copyright 2015 The Arsenal Football Club plc. Permission to use quotations from this article is granted subject to appropriate credit being given to www.arsenal.com as the source