Theo Walcott has flown home from Arsenal's pre-season training camp in Germany to undergo a scan on his ankle.
Walcott, an England international midfielder, is thought to have suffered a recurrence of an old injury, and Arsenal manager Arsene Wenger is keen to diagnose the problem ahead of the new Premier League campaign.
"Theo went home early and was due to have an MRI on Tuesday," Wenger told Arsenal's official website. "It is an old ankle injury from the end of last season. It's one that comes and goes.
"We need some more investigation because sometimes he's completely free of it and sometimes it affects him. But we had to send him back because he couldn't practice anymore."
Walcott is now a serious concern ahead of Arsenal's Premier League opener against Newcastle on August 13.
Gunners forward Andrey Arshavin, meanwhile, has outlined his goals target for the forthcoming season after netting ten times last campaign. He told the club's Official Souvenir Programme: "My own target is simple - I would like to score 15 goals in total."
The Russian also believes Arsenal will be a more powerful force in 2011-12. He said: "I think we will get stronger and stronger. In particular I think our work on set-pieces, both attacking and defending, will be better. We'll also play a pressing game - if we do that well, I'm sure you'll see an improved team."