I pick Medvedev to win in four sets, due to several reasons most of which are already mentioned by others.
1. Medvedev though appears to be dying, will recover and play well thanks to the 2-day break.
2. Grigor's previous match mostly involved a loss by his opponent rather than winning by GD due to his brilliant play.
Of course, he had to hang in there without folding and he did hold up his end regarding that part.
3. Going back to the first round, Grigor has not really faced any tough opponent, unlike DM.
4. Finally, Medvedeve will get energy from crowd, either because they suddenly support him or because they continue to oppose him.