Arsenal could be without Cesc Fabregas against Porto on Tuesday night after he suffered a recurrence of his hamstring problem.
The Spanish ace has been dogged by a hamstring injury all season and had to substituted again after scoring the opening goal in Saturday's 3-1 win over Burnley.
Gunners boss Arsene Wenger is now waiting to discover the full extent of the damage but he is an early doubt for the crucial Champions League game at the Emirates Stadium.
"He has a hamstring problem and how big the damage is we don't know yet because it's too early," Wenger revealed. "We have to make a late decision over whether he plays on Tuesday, certainly.
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It is the same hamstring [he hurt earlier in the season]."