Stopping the right uppercut ?

[Andre]

He is a southy?
Go for the crook of his right arm and land your left hand open in the crook of his arm like a partial open grab (no thumb involved) then move in with his arm under control,if you can drag his arm down even a touch it will stop him raising his front foot too; then as he reacts you turn your left arm over into an elbow to his face,your hand still on his elbow for control as you roll on in with the left elbow to the face with full body movement behind it like a ram. Take his front right foot with your left foot (even sweep it back sohis leg gets pulled forwards) or just shift it slightly as you land the elbow and he'll also be going for re balance which'll allow you to punish him right on his reaction once again. (maybe with your own uppercut right there as he flails for that millisecond.

You could also try the side step and land a chest punch a cross and into the crook of his right arm. drop your hand down into the elbow for control of his balance as you move in.

Or maybe jab then instantly drop your elbow down into his uppercut as you move in.

The elbow point will control his balance and stop that side firing off, the rules are on your side in MMA for you to practice that and utilize it for setting up your combos,you will feel where he is going in reaction so then you push him there and catch him in his next reaction.