Arsenal boss Arsene Wenger has been left 'surprised and worried' after Theo Walcott suffered an injury setback.
The speedy winger only recently returned to action after a long-term shoulder injury he sustained while on international duty with England.
Walcott made his first start for the Gunners since the problem last weekend and impressed during the 4-0 triumph over Blackburn Rovers.
However, the 20-year-old has damaged his knee during a training session prior to Saturday's trip to Newcastle United and now faces a nervous wait over a scan.
Very bad news
"Walcott got injured today in training," Wenger told the club's official website. "We have to test it, he has a scan on his knee today.
"We are surprised and worried. He was in very good form coming back and that is very bad news for us and for England.
"For the rest of the season might be too long, but he's out of tomorrow's squad and he could be out of the England squad.
"He locked his knee so it could be a cartilage problem. He did it walking back from training. He was fully normal during training but maybe it only came out when he stopped.
"We have to see how he responds today and I hope it's not really serious."