Petrov kept up his recent scoring run with City’s second goal - making it three in his last three appearances - but a knee injury means he could miss out on the fourth-round game.
The Bulgaria winger was expected to step down for fit-again Craig Bellamy against Fulham but instead it was England’s Shaun Wright-Phillips who made way.
Manager Mark Hughes said: “I felt it was important for Martin to play. He’s been doing well and I didn’t want to disappoint him. He was keen to get the ball and scored what should have been the winner.
“But he got a bang on the knee and was unable to finish. It’s been sore for a while now. Hopefully it won’t be too serious, a bang and not a twist.”
Skipper Kolo Toure, who scored the extra-time winner in the last round, is doubtful to face Scunthorpe after landing badly on his troublesome heel, while Roque Santa Cruz was taken ill with tonsilitis on Saturday night.
