Manchester United manager Ole Gunnar Solskjaer has labelled his side's first-half performance in Tuesday's League Cup semi-final, first leg defeat their worst display of the season.

Despite starting the game without a recognised striker, holders City outclassed United in a 3-1 victory at Old Trafford, scoring all three goals in a 21-minute first half blitz.

The performance led the Norwegian to question his squad's mental attitude, saying the players needed to learn to spur themselves on when things went against them.

"From their goal until halftime is the worst we've played," Solskjaer told reporters. "From the first goal until halftime we couldn't cope. We let them play, our heads dropped, we made decisions we shouldn't and it needed sorting at half time.

"It's natural your head goes down when you feel you're not performing, but we've got to get out of it quicker... It can't be me coming in at halftime, that's the learning this team (must do).

"We've got a young team. I've said it a few times but it's not going to change between every press conference, that statement. I'm still in that phase. It's a young team and we're learning and these experiences must stick."

Solskjaer replaced Jesse Lingard with Nemanja Matic at the break to shore up the midfield and they managed to get a foothold in the match with a Marcus Rashford goal, keeping the tie alive ahead of the second leg later this month.

"The second half was a good response, (but) it's a steep mountain to climb," Solskjaer added. "The second half gives me something to believe in because it's respectable and a good second half."

Solskjaer said injured centre back Harry Maguire, who did not play after failing a fitness test, may not be ready for the weekend's Premier League home game against Norwich City.