The 26-year-old has struggled with injuries over the past 12 months and picked up a muscle problem while on World Cup duty with Argentina that has hampered his pre-season preparations.
But the former Atletico Madrid striker has been working hard to get fit behind the scenes, having not featured in any of City's pre-season friendlies, and Pellegrini has not ruled out a return to action in Sunday's clash at St James' Park.
"We will see [if he plays] on Sunday," he told reporters. "I am not so sure if he will or will not."
France international Eliaquim Mangala, meanwhile, is unlikely to make his City debut against Alan Pardew's side, with Pellegrini insisting that he needs to build up his fitness before he can be involved.
"Mangala needs to work more with the team to be able to play," he added. "Maybe he will not play this weekend.
"He has had so many months without playing normally so we are trying to make a mix for him: a mix of pre-season training and trying to get him to our level to play for the team."