Former Manchester United striker Wayne Rooney insists Manchester City have work to do before they can be called the Premier League's best ever team.

Rooney, who left United this summer to rejoin boyhood club Everton, believes that Pep Guardiola's all-conquering team (who have picked up 17 wins from 18 games so far in the league) still need to follow through on their amazing start to the season by winning trophies.

"I'm not sure they [City] are quite there. They would have to keep going and do a lot more," Rooney told TalkSPORT. "There have been so many great teams throughout the years in the Premier League. This City team needs to win trophies and needs 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!"

City have been compared to Arsenal's "Invincibles" of 2003-04 who went a whole Premier League campaign undefeated, but Rooney says that it is much harder to do now than it was back then.

"I don't think they can go unbeaten," he added. "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.

"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.

"But now there are five or six other teams that can all beat each other and I'm sure in one of those games Man City will get beaten."