Pratt suffered a knock to the knee in the second quarter when he was tackled by Magpie Dane Swan.
He went straight to the rooms and emerged about 15 minutes later with ice strapped to the knee.
He was able to walk around but is unlikely to return to the game.
It was better news for Collingwood, with Paul Medhurst returning from an ankle injury in the first quarter to have seven touches in the second term.
Medhurst limped from the ground with an sore right ankle 13 minutes in to the match and went straight down to the rooms.
