Out of all the players, he's the one who plays with the biggest lack of energy and what seem to be a lack of will. Its almost like he doesn't want to be there. A minute after coming on at the weekend he made a half hearted attempt at a clearance and then he stood there not pressing the opposite team's player he had just given the ball to (I think it was the whole stretch of play that led to the penalty).
There was also the whole incident with Klopp a few games ago (don't remember who was the opposition) where he burst a lung shouting at him from the sideline and the lad did not seem to care too much. A couple of games after that the gaffer decided to play a double pivot and completely omit him from he starting lineup which is telling.
I know the defensive side of Thiago's game is very underrated, but he's not supposed to look like the better DM when Fabinho is on the pitch. Except for a couple of games, Fabinho has looked like a cone for me. Not much movement, doesn't press much, doesn't run much, doesn't jump much, etc.