The defender was stretchered off when he landed awkwardly after challenging Spurs' Benoit Assou-Ekotto for an aerial ball.
"We are very worried about his injury," Wenger told the club's official website.
"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."