Ole Gunnar Solskjaer felt Manchester United's first half against Manchester City in the Carabao Cup on Tuesday was the worst they have played this season.
City dominated the first leg of the semi-final at Old Trafford, where Bernardo Silva and Riyad Mahrez scored before Andreas Pereira's own goal.
Marcus Rashford struck in the second half for United, to give them a glimmer of hope heading to the Etihad Stadium on January 29 despite the 3-1 loss.
Solskjaer was unhappy with the way his side started, lamenting their first half – particularly after Silva's fine 17th-minute opener.
"From their goal until half-time it's the worst we've played," he told a news conference.
"Before then, it could've gone either way, a goal, but that doesn't matter now.
"We've just got to focus on Saturday, Norwich [City]. After that second half, we've got something that we can believe in."
The second leg of the semi-final will take place at the Etihad Stadium on January 29 with the Red Devils facing an uphill battle to turn the tie around.