Quality is no factor if you don't get the chance to show it, ask Pepe. If he comes back it'll be on the bench and he better hope he hits the ground running when he does get games, any mistake he goes back and his form nosedives.
I know you don't like to hear this but Mustafi used to be a top class defender for Valencia. Even ignoring the difference in Ligue 1 and PL it's not a given that looking good elsewhere means you'll do well here.
