That's kind of a lame excuse to me. This is a player he's never seen/coached before, why experiment with him the first chance you get when it's clear he's better on the right? That's so hasty and unnecessary. At least make that a secondary objective after letting him get comfortable in his natural role in a new team.
He returned to play at the end of the match on the right side, but lost the ball that brings Milan's goal back to his best position.