Xavier point guard Edmond Sumner left Sunday's 82-77 win at St. John's in the second half with what appeared to be a serious knee injury.

He did not return.

Here's video of the injury:

(Warning: The video is graphic.)

"We don't know yet," Xavier coach Chris Mack reportedly said on his postgame radio show. But, needless to say, it doesn't look good. Anything short of a season-ending injury would probably be surprising.

An MRI is scheduled for Monday.

Sumner was averaging 14.9 points, 4.9 assists and 4.4 rebounds before Sunday's game at St. John's. That makes him Xavier's second-leading scorer and third-leading rebounder -- and he's leading the team in assists.

Xavier is 15-6 and ranked 22nd in the Top 25 (and one).

The Musketeers' next game is Wednesday against Seton Hall.