Zeise of the PG called it an

Johnson, however, was injured with about 5:52 to play in regulation and that forced the home Dukes to play down the stretch without their best player and most experienced player.
Johnson actually needed to be carried off the court after the game as he was not able to put pressure on his leg.

DU website and the Trib said cramps.

Ferry was non-commital in the post game radio show.   He did not say cramps.  He said more like a "We'll see if he can go response."   

Needless to say, I hope he is okay.