No. I think rules are pretty clear you can't force a procedure on a player. That being said, they don't have to send him out there to pitch.
So create a standoff: you can't pitch until you get an MRI, and he continues to refuse to MRI. In which case he never pitches again (until one side or the other gives in). Mets were in a tough situation; might as well send him out there and see what happens.
