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."
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