The Northern Ireland international limped out of the 2-1 win against Blackburn on Saturday and must now wait for news on the problem.
The injury is suspected to be a recurrence of the ankle problem that the 21-year-old picked up in the Carling Cup semi-final second leg against Derby.
Evans missed five games with the injury before returning for the 3-0 win over Fulham last Wednesday.
The youngster will be missed by Sir Alex Ferguson's team with fellow defenders Nemanja Vidic suspended for the Inter match and Wes Brown and Gary Neville out through injury while John O'Shea may have to be rushed back from a heel injury.
Recurrence"It is a recurrence of the ankle injury I had before and is a bit tender," Evans revealed to the Manchester Evening News.
"I caught it when I kicked the ground during the game. At this point, I don't know whether I will be fit for the San Siro.
"The doctor said he will have a look at it, and he will have a better picture then."
Meanwhile Ferguson added: "We are having a nightmare with defenders this season.
"The defenders are being changed all the time. You reach a point when you start to find it hard."