Frank Lampard's future became the subject of fresh speculation after he sent Manchester City into a tie atop the Premier League standings with the winning goal in Thursday's 3-2 victory over Sunderland.

Lampard came off the bench to score in the 73rd-minute, hours after City confirmed he will remain at the club until the end of the season.

City officials said Lampard has been loaned to the club from Major League Soccer's New York City FC, which he joined after leaving Chelsea at the end of last season.

Lampard had initially been due to join up with the US squad on Jan 1, but it emerged that he has signed an extension to the short-term contract that saw him join Manuel Pellegrini's squad in August.

It calls into question the exact nature of Lampard's contract with New York City and when asked whether the 36-year-old midfielder would ever play for the MLS side, Pellegrini refused to answer.

"We are only finishing December," the Chilean said. "I think you can't have all different questions about Frank Lampard.

"Frank will stay now with us until the end of the season. In the month of May, you can start thinking about what will happen in the future."

New York City supporters have been vocal in their dissatisfaction with City's handling of the Lampard affair, even though the club has yet to play a game.

A statement from supporters' group the Third Rail claimed Mansour bin Zayed Al Nayhan, who owns both clubs, was treating the New York version as an inferior member of his soccer stable.

But Pellegrini said that even if City was to exit the Champions League knockout stages early, there is no possibility of Lampard making a move across the Atlantic before May.

"That's why, every time you asked me what was happening about Frank Lampard in December, I repeated that we were trying to keep Frank, but it was not easy because other people, other clubs were involved in this situation," he said.

"I understand perfectly New York fans want to see Frank playing because for the fans to see him playing in New York would be amazing.

"I hope he will be there next year, but I think at this moment it is the best decision for him, for the club, for New York, for him to stay here with us until the end of the season."

Lampard scored a dramatic winning goal, his fifth of the league season, three minutes after coming on against Sunderland after his side squandered a lead handed to it by Yaya Toure and Stevan Jovetic.