LONDON - Manchester City manager Roberto Mancini has singled out the one thing that could cost his side the Premier League title this season - the failure to sign Robin van Persie.

Van Persie joined City's big rival, Manchester United, from Arsenal in the summer and has scored 14 goals in 20 games so far this season.

"Robin van Persie is a very important player for United," Mancini said, before yesterday's 3-0 win against Stoke City (see IHT for full coverage ). "He has changed their situation. He is the difference between us."

As van Persie has prospered, champion City sits second, seven points behind, and Mancini said the Dutchman had been close to joining him at Eastlands.

"We were very close three or four months before he joined United," Mancini said. "We wanted van Persie because we knew he could be an important player. "He is totally different from our other strikers. We wanted him for the Champions League and for the Premier League.

"We were sure he was for us but this did not happen and now we can do nothing."

Mancini said he was confident his strikers - Sergio Aguero, Carlos Tevez, Edin Dzeko and Mario Balotelli - were good enough to help City retain its title, but will now have to do without Aguero, who suffered an injury yesterday.

"I am happy, very happy," he said. "Last year we were the team that scored the most goals in the Premier League. "But when you can improve your team with another top player, this is important. With van Persie we would play with three strikers sometimes."