Pep Guardiola says Manchester City "don't have a chance" of beating rivals Manchester United at the weekend if they repeat the performance that saw them eliminated from the EFL Cup.
City started with the likes of Erling Haaland, Kevin De Bruyne and Ederson among their substitutes for Wednesday's quarter-final tie at Southampton and were made to pay in a 2-0 defeat.
Sekou Mara put the Saints ahead when beating Kyle Walker to a cross, before Moussa Djenepo profited from Stefan Ortega's poor positioning to add a second before half-time.
De Bruyne was introduced as part of a triple substitution at the interval, while Haaland followed soon after, but City failed to register a shot on target for the first time this term.
Next up for City is a trip to in-form United in the league on Saturday, and Guardiola accepts a big improvement is needed from his side at Old Trafford.
"It's a different competition, but of course if we perform in this way we don't have a chance," he said in his post-match press conference. "I know the momentum they have.
"For many years they're looking forward to being in this position. We know exactly what to do to play better and we're going to try to do it."
Asked about his decision to leave out Haaland and De Bruyne for a second game running, Guardiola said: "Who knows if with Erling and Kevin it would have been different?
"But when you play for four competitions it's important to use every player in the squad."
City suffered defeat inside 90 minutes of an EFL Cup tie for just the third time in 30 matches under Guardiola, who has won the competition four times in seven seasons.
The loss – City's fourth in 28 games this campaign – came just three days on from a superb performance in seeing off Chelsea 4-0 in third round of the FA Cup.
And Guardiola accepts there could be no complaints with his side's two-goal reverse at St Mary's Stadium.
"It was a bad night. I know them quite well. We didn't get close to what we are," he said. "Three days after facing Chelsea... I've nothing to say.
"They were better, we congratulate them and accept it. We have to be prepared every single game when you play for Manchester City. Today we were not."
City defeated United 6-3 when the sides last met in October and are seeking a Premier League double over the Red Devils in a single season for the sixth time ever.
Ilkay Gundogan, who played the full 90 minutes against Southampton, is hoping the cup setback can spark some life into City heading into the derby.
"There's no room for any mistakes [against United], or for any poor performances like today," he told the club's official website.
"Hopefully, if there is something good we can take out of this game today, it was something like a wake-up call at the right time.
"Even though it is sad and disappointing to be out of this cup, hopefully, at the end, in a few weeks we can at least look back and take something good out of this game."