Lampard scored a late equaliser for City in their 1-1 draw at home to Chelsea in the Premier League on Sunday. It was his first appearance against Chelsea since he ended his 13-year association with the club in June.
The 36-year-old former England midfielder is due to link up with parent club New York City FC in January, but Pellegrini says he could feature in City’s return fixture against Chelsea at Stamford Bridge.
“Frank will stay until January because until January he doesn’t have anything to do in the United States because they are not working,” Pellegrini told a press conference.
“In January, we will see what happens here and make a decision. It is not a problem in this moment.”
Pellegrini also played down reports in the British media linking City with a move for Everton playmaker Ross Barkley.
“I don’t talk about rumours. We are not trying to bring anyone to our squad at this moment,” he said.
“We have an important restriction on money and the amount of players we can have in our squad (due to Financial Fair Play sanctions). I don’t know where the news comes from, but for here in Manchester City it is not a problem at this moment. We have the squad. I am not looking at any other players.”
City begin their defence of the League Cup away to second-tier Sheffield Wednesday on Wednesday, with right-back Pablo Zabaleta unavailable due to suspension.
David Silva (ankle) and Sergio Aguero (knee) have both been ruled out due to minor injuries, but Pellegrini said that they will return for Saturday’s league game at Hull City.