City suffered a fourth defeat of the domestic season at home to local rivals Manchester United last weekend, leaving them 14 points behind runaway leaders Liverpool after 16 matches.

Gundogan was a key member of the side that edged out Jurgen Klopp's men in an unrelenting battle last time around but feels standards have clearly slipped this term.

Asked how far City are from their best form ahead of Wednesday's Champions League match at Dinamo Zagreb, Gundogan told BT Sport: "Quite far, to be honest.

"Obviously it's so far a difficult season for us. There's already a huge gap in the Premier League between Liverpool and us.

"We can't deny that the title race is already over for us, so we have to compete to qualify for the Champions League again next season.

"That's disappointing, to be honest. Also, this early in the season to have such a huge gap is something that we're not really used to."

Pep Guardiola's team won the Premier League with a record 100 points in 2017-18 and backed that up with haul of 98 last time around.

Gundogan does not feel there is any discernible difference in the atmosphere among the City squad, but conceded this could be interpreted as a sign of complacency or staleness.

"I don't feel like the dynamic in the group is worse than it was before. I think it's still similar," he said

"Maybe that's also a problem, that it's too similar. Maybe there needs to be a change.

"I don’t really know to be honest, I just think that the next weeks will show us and prove to us the right way to go.

"If you don't know the feeling of frustration, of anger, of disappointment, I ask myself sometimes: 'What is it really worth to be successful? What is it worth to be happy?'.

"Obviously we need these emotions."

City are already through to the last-16 of the Champions League as Group C winners and Gundogan will start the dead rubber in Zagreb as part of a much-changed side featuring teenagers Phil Foden and Eric Garcia.

"No one says that if you are not successful in the Premier League you cannot be successful in the Champions League," he added. "In the Champions League, all chances are open."