Manchester United goalkeeper Andre Onana questioned Manchester City's penalty for their opening goal on Sunday.
City cruised to a 3-0 win at Old Trafford, with scoring being opened by a first-half penalty awarded for a Rasmus Hojlund's foul on Rodri.
Onana said: "It is not how we want. We played a very good opponent and unfortunately we didn't read the game.
"As Manchester United we try to be ready every game but there were some key moments - like the penalty.
"I'm not the one to decide and we have to accept the decision of the referee.
"The first goal was a key moment and from there on we looked down."