Arsenal boss Arsene Wenger is 'very worried' about the injury suffered by Bacary Sagna in the North London derby and expects to learn the extent of the damage on Sunday night.
The France international was undergoing assessment in a hospital after being stretchered off in the defeat to Tottenham following a bad fall in the second half.
Sagna came off second best in a challenge with Benoit Assou-Ekotto and Wenger has implied the Spurs full-back is to blame.
It is feared Sagna has fractured a fibula bone, which could require an operation and an estimated three months of rehabilitation.
"We are very worried about his injury," said the Arsenal boss in his post-match press conference.
"He is in hospital at the moment and it is too early to say but the first signs do not look good at all.
"It is the fibula in the ankle that has to be checked, that is what I have been told. We will know tonight.
"I think he was pushed quite hard by Assou-Ekotto and I'm not sure what happened to him.
"He might have landed the wrong way, I don't know. I will have to see it again. Straight away he wanted to be substituted."
Wenger's team have made a terrible start to the season, which has already seen the club lose four Premier League matches to leave them in 15th position.
Sagna seems certain to be ruled out of France's forthcoming Euro 2012 qualifying double-header against Albania on Friday and versus Bosnia on 11th October.
And Wenger, whose team next host Sunderland after the international break, will nervously await an update on the full diagnosis of one of his best players.