Manchester City defender Pablo Zabaleta has conceded the struggling English champions face a battle just to finish fourth in this season's Premier League.

City's hopes of a successful title defence had all but evaporated before Sunday's derby and a 4-2 defeat by Manchester United left Manuel Pellegrini's men 12 points behind leaders Chelsea, who have a match in hand, with just six games left to play.

But a sixth defeat in eight games in all competitions left them in fourth place and knowing they cannot afford to slip any lower if they are to play in next season's Champions League.

And if City's slump continues it's still possible for the likes of Southampton and Liverpool to overhaul them before the end of the season.

Yet New Year's Day saw City draw level on points with Chelsea at the summit after a 3-2 win over Sunderland.

"It is time to analyse what we are doing wrong and try to improve for the next few games," Zabaleta told reporters after the derby defeat.

"There are still 18 points to play for and we must be honest with ourselves and start to push hard, play better and win games, so we can get in the top four.

"When you lose those games it is always really hard, but that is football sometimes. Football is about momentum.

"It seems you lose confidence when you cannot get results and it was a really tough afternoon."

City made a fine start to their bid for a fifth successive derby win when Sergio Aguero put them 1-0 up in just the eighth minute.

But it did not take long for United to equalise through Ashley Young and Louis van Gaal's men pulled away through goals from Marouane Fellaini, Juan Mata and Chris Smalling secured a convincing win before Aguero's 100th City goal reduced the deficit late on.

"It seems we lost confidence and were nervous," said Zabaleta. "Then it was hard for the team to react and we conceded the second goal.

"In the second half we didn't create many chances and when United scored the third goal the game was over."

Meanwhile City winger Jesus Navas was equally bemused by the way the team were undone by United.

"I don't really know (what happened)," the Spaniard said. "They scored the equaliser and they were back in the game. We started strong but it wasn't our day and we need to focus on the upcoming games.

"It's Champions League (qualification at stake) so we have to fight until the end to be in the top four."