Arsenal winger Theo Walcott is out of tomorrow's trip to Newcastle United after suffering an injury in training.

The 20-year-old is also a major doubt for England Under-21's clash against Norway next week after locking his knee walking back to the changing rooms following this morning's session at London Colney.

Walcott had only just returned from a four-month absence during which he underwent shoulder surgery and will await the results of this afternoon's scan to determine the extent of his latest setback.

Arsenal boss Arsene Wenger said: "The bad news for us and for England is that Walcott got injured today in training. We are a bit surprised and worried because he was in very good form.

"It's certainly very bad news for us. It would be too much to say he is out for the rest of the season, but he is definitely out of the squad for tomorrow.

"He will be scanned and we will assess his situation tonight. He locked his knee so it could be a cartilage.

"He was walking back from training - maybe he has done it in training and it came out when he stopped."

Wenger also defended captain Cesc Fabregas against accusations he spat at Hull assistant manager Brian Horton following Tuesday night's FA Cup quarter-final victory at Emirates Stadium.

The Gunners boss insists the club will cooperate with any Football Association investigation and defended Fabregas's right to sit with the players in plain clothes, despite not being part of the squad.

"I have spoken to Cesc," he said. "He denies categorically what has been asserted by Hull. We are open to any investigation from the FA. If they want to take the matter further we'll co-operate fully, like we always do, and for me that is the end of the matter.

"All of the first-team squad who weren't playing were behind the bench and I think it's completely normal that they share the victory with the players on the pitch. He was free to dress how he wanted.

"Cesc should be fit in two weeks. He is back in full training now and during the international break he has two weeks to sharpen up. Normally, he should be available again against Manchester City."

Striker Eduardo (calf) and goalkeeper Manuel Almunia (ankle) are both fit to face the Magpies.