Premier League champion City trails leader Liverpool by 14 points after defeat in the Manchester derby on Sunday (AEDT).

Third-placed City's total of 32 points is also Pep Guardiola's worst points return after the first 16 matches of a top-flight season in his managerial career.

City briefly turns its attentions to a UEFA Champions League clash with Dinamo Zagreb on Thursday, having already qualified for the knockout stage as Group C winner.

However, league matters were not far from Gundogan's mind at a news conference ahead of their final European group-stage match.

"First of all, I think that it's nothing very unusual," Gundogan said of City's struggles.

"After having two great seasons, it's even tougher to perform the third one in a row. It's a challenge to stay on top and play the same kind of successful football every season.

"I think it's normal that we go through this period, and the only way out of it is to stick together [and for] every single player to take the responsibility to reach his best level again."

Gundogan vowed City's players would work hard to reignite their season, even though Guardiola has recognised it is "not realistic" to catch Liverpool.

"The sooner we can do it, the sooner we will be successful again. That's the challenge," the 29-year-old explained.

"It's normal, in football and in life. If you're successful and you've won so many things, sometimes you lose a little bit of focus.

"But the more defeats you get, the more you recognise that's not the way you want to end up. you want to improve again and get to the level you already were.

"I think we all want to be successful and we all want to reach for the best, because the potential is definitely there."

Gundogan acknowledged City's form has hit morale but claimed they have a strong mindset to overcome such setbacks.

"Of course, there's a lack of confidence when you lose game and you recognise you didn't play as well as you could play," he added.

"I think we are strong, especially mentally. We should be able to do our best in every single game.

"The game starts from zero. It's just about improving ourselves and putting in a good performance on the pitch to try to win the game."