The Spanish giants lost their first home game in 25 matches when beaten by 1-0 Sporting Gijon at the weekend, giving Spurs hope of a securing a famous result in the Bernabeu on Tuesday night.
Wenger believes Harry Redknapp's men have nothing to lose.
The Arsenal manager said: "It is very open, it is 50-50.
"Who cannot be beaten? If everything went all right, Barcelona would be out today. If it had stayed 11 v 11 (against Arsenal), I am convinced of that.
"Why can't Spurs beat Real Madrid. Real Madrid has a disadvantage to play the first game at home, Spurs at home look to be strong. It is a real 50-50 game."
Source: PA
Source: PA