this is mainly down to sharpness + fitness. Players who aren't playing regularly won't be at their peak athleticism.
While he's obviously not going to be a "quick" player, he never had this issue in the CL against the likes of Juventus, Real Madrid and Tottenham.
The proof is there that he CAN operate at that level, so what is the difference?. Let's not act like he was supposed to be dominating this match single handedly either, Ndidi and Tielemans are 2 of the best CM's in the league.
Just like Fred, he's obviously taking time to adjust to the pace of the league. In the PL teams shut you down ASAP and don't give you time to dwell on the ball, other leagues retain shape and make you pass through them but it gives you more time to think.
Before we become too judgemental we need to give him a chance to have a break, hit it again next year and see if he can come back fighting. I know he is a very good player, but will he be able to handle the speed? that's the question.
He had a perfectly fine first half but people here can't seem to acknowledge that either.