Nope, he's fine. His positioning and awareness are great. He's good but not exceptional in the air, which is why we brought in Lovren. Most ball-playing teams play a tall, strong centre half alongside a quicker one who can read trouble and mop it up - see Vidic and Ferdinand, arguably the model pairing for a successful Premier League team.
If we are after one more signing for the starting XI then centre back might be a good choice, but I don't think we are and don't think we need to be.