Evans had had a longterm problem of his knee locking up on him, but it usually resolved quickly and rarely cost him playing time.
However, Evans hasn't played since the World Cup break, and coach Sigi Schmid said today that he might be done for the year.
"His injury is not responding," Schmid said. "It's a strange injury again, it's not something that you normally see. He's a pretty tough kid, he fights through things. He was really struggling (Friday) at training: He pulled himself out. So we've got to look at maybe going a different direction to solving it. So, it might take him out for a longer time. It might take him out for the season. But that's something that we'll be able to determine early next week."