If Manchester City exhibits the same level of play that saw them knocked from the Carabao Cup, Pep Guardiola claims they "don't have a chance" to defeat rival Manchester United this weekend.

For Wednesday's quarterfinal match at Southampton, City started with players like Erling Haaland, Kevin De Bruyne, and Ederson among their replacements, and they paid the price with a 2-0 loss.

Sekou Mara gave the Saints the lead by beating Kyle Walker to a cross, and Moussa Djenepo added a second goal just before halftime by taking advantage of Stefan Ortega's poor positioning.

De Bruyne and Haaland were substituted in during the break as part of a triple substitution, but City went the whole second half without a shot on goal for the first time this season.

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."

For the third time in 30 games under Guardiola, who has won the EFL Cup four times in seven seasons, City was defeated before the end of the 90-minute mark.

The defeat, City's fourth in 28 games this season, came just three days after an outstanding display that saw off Chelsea 4-0 in the FA Cup third round.

Guardiola acknowledges that his team's two-goal loss at St. Mary's Stadium could not be criticized.

"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."