Wayne Rooney believes Manchester United's Champions League winning side in 2008 was better than the current City side.
Pep Guardiola's men made it 16 wins on the spin following a 4-1 victory over Tottenham at the Etihad.
City have now dropped just two points all season - in the 1-1 draw with Everton when former United skipper Rooney found the net.
There have been some suggestions that this City side could be the greatest to grace the Premier League but Rooney insists that is premature.
"There have been so many great teams in the Premier League. I'm not sure City are quite there," he told talkSPORT.
"They need to win trophies and to do it for a longer period to be in that bracket.
"The best ever? I would go with the Man United team from 2008."
Rooney was part of the United side under Sir Alex Ferguson that won the Premier League and Champions League.
Meanwhile, he has played down suggestions the City side will go unbeaten for the rest of the campaign.
"They have done incredibly well with the run they have been on, but the Premier League is so difficult, especially now with this Christmas period coming up," he added.
“I know they have a huge squad, a great squad of players. But there are so many top teams. I think in previous years it has been two teams and you went in knowing you would win most of the other games."