Walcott has made only two starts since coming back from a shoulder injury
Arsenal star Theo Walcott could be set for another spell on the sidelines after a knee injury ruled him out of next week's Under-21 internationals.
The 20-year-old has only just recovered from a shoulder injury sustained in training with England in November.
"Theo locked his knee when he was walking back from training, so it could be a cartilage," said Gunners boss Arsene Wenger.
Walcott is set for a scan on Friday to assess the extent of any damage.
It had been hoped Walcott could be eased back into action with the Under-21s against Norway and France, while the senior squad play a Slovakia friendly and a World Cup qualifier against Ukraine in the same period.
But Walcott, who scored a hat-trick for England against Croatia in a World Cup qualifier last year, now faces another, as yet undetermined, period out of action.
Wenger continued: "Out for the rest of the season would be too long, but certainly he is out of the squad for the Newcastle game tomorrow.
"Maybe he has done it in training and it came out when he stopped, but we have to see how he responds.
"I hope that it is not serious because he was in very good form coming back."
Stuart Pearce has not yet revealed whether he will call up a replacement to the U21s, but he does also have Aaron Lennon at his disposal for the warm-up matches ahead of this summer's European Championship.
However, Pearce has called up Ryan Shawcross to replace Newcastle's Steven Taylor, who was injured in the Magpies' 3-1 defeat against Arsenal on Saturday.
"We wanted to take on a Scandinavian side as we've got Finland in the European Championships so Norway was a good option," Pearce said.
"On top of that we wanted another 'A-line' nation that hadn't reached the finals and they don't come much better than France, so it's a fantastic game for us.
"The two games will give us a full 10 days to work together. We can work on various things, both in the games and on the training pitch.
"It's not often you get the chance to have that length of time with the players and it'll be a vital period to prepare for the summer."
England U21 squad:
Goalkeepers Joe Hart, Scott Loach, Joe Lewis
Defenders Kieran Gibbs, Michael Mancienne, Nedum Onuoha, Micah Richards, Andrew Taylor, Steven Taylor, David Wheater
Midfielders Lee Cattermole, Craig Gardner, Tom Huddlestone, Adam Johnson, Aaron Lennon, James Milner, Fabrice Muamba, Mark Noble, Jamie O'Hara, Jack Rodwell
Forwards Fraizer Campbell, Matt Derbyshire, Sylvan Ebanks-Blake, Daniel Welbeck
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