The 36-year old midfielder is on loan with the reigning Premier League champions until the New Year but there have been suggestions that he could extend his stay at the Etihad Stadium.
Pellegrini was quizzed on whether or not Lampard would remain at Eastlands beyond his initial spell but was unable to offer any further insight into the possibility of the ex-England international staying on after January 1.
"When we have to make a decision, we will make a decision," said the City boss.
Former Chelsea star Lampard signed with MLS expansion franchise New York City FC in July this year and is due to link up with the club early in 2015 as they prepare for their debut campaign in the USA and Canada's top flight.
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