Arsenal striker Robin van Persie is facing a month on the sidelines after twisting his knee on international duty with Holland this week.

Initial reports suggested van Persie would be out for four weeks and Gunners boss Arsene Wenger admits that looks like being an accurate diagnosis.

"It looks like a knee injury," Wenger told Arsenal TV online.

"We will know later how bad it is but the early signs are that he will not be able to perform for us in the next four weeks.

"It is a big blow. Robin is a striker, a supportive striker and important on set pieces as well.

"I hope he will be back soon and we'll do the maximum to get him back."

Arsenal also confirmed that Philippe Senderos picked up a back injury playing for Switzerland and would be out for two weeks.