Silva was forced off in the first half at the Etihad Stadium due to a knee injury, and could now miss Sunday's clash with Manchester United in the Premier League.
Pellegrini refused to reveal any more details about the Spaniard's condition, while also defending his decision to play one of his key players from the start.
"We will see tomorrow with the doctor and I can't tell you at this moment," the Chilean told reporters. "David has a problem with his knee and I don't know how serious it is.
"There was no reason why David could not play. We played on Saturday, he had four days to recover, David was perfect to play, so there was no reason not to play him. He was prepared to play."
Yaya Toure was removed in the second half against the Magpies with a groin problem, but Pellegrini revealed in his post-match press conference that the substitution was to avoid causing further injury.