David Silva could miss Man City's Premier League title run-in after being stretchered off in the second half of Monday night's 3-1 win over West Bromwich Albion at the Etihad Stadium.
Silva suffered a recurrence of a recent ankle problem and City's medical staff will spend Tuesday determining whether the Spaniard will be fit enough to play some part in his team's last four games of the season.
Silva's injury soured a businesslike 3-1 win over the relegation-threatened Baggies with two goals inside the first 10 minutes from Pablo Zabaleta and Sergio Aguero settling nerves before Martin Demichelis added a third after Graham Dorrans had briefly reduced the deficit.
Pellegrini said: "We will see tomorrow (Tuesday) what has happened. David played the last three games with pain in his ankle and that is why it wasn't possible for him to play against Sunderland (last week).
"He got a kick some weeks ago and every week he has played the game with pain. It is hard to tell without the doctors giving their assessment but hopefully it will be a short-term injury."
The win maintained City's title hopes as it moved them within six points of leaders Liverpool with one game still in hand.
There was little chance of a repeat of last Wednesday's frustrating 2-2 home draw with Sunderland after Zabaleta headed the opener when Baggies keeper Ben Foster palmed Aguero's initial effort into his path.
Aguero hit a sweetly struck second and it looked like being a night of damage limitation for the Baggies, whose defeat leaves them precariously placed three points above the drop zone going into Saturday's crucial home clash with West Ham.
But a brilliant strike from Dorrans gave the visitors hope and they even thought they had drawn level when Matej Vydra bundled the ball home only to be ruled narrowly offside.
Demichelis knocked home a Samir Nasri corner to restore City's two-goal cushion and in a much more low-key second period Foster had to be alert to deny both Dzeko and City substitute James Milner.
Baggies boss Pepe Mel has injury concerns of his own heading into the crucial game against the Hammers after defender Liam Ridgewell limped off in the closing stages with a knee injury.
Ridgewell is yet to be assessed by Hawthorns medical staff but Mel intimated the initial prognosis was not good, saying: "We have a feeling he may go on to miss the rest of the season. We will have a look at the tests tomorrow but the feeling is he won't be able to play."
Mel added: "The most important thing we can do is focus on Saturday which is really like a final for us.
"It really was as difficult game after conceding in the third and 10th minutes and we had to change everything we'd been working on during the week. After that the team did really well."