Collingwood forward Lachie Sullivan was subbed out of the Pies win over Richmond at the MCG with a suspected PCL injury on Sunday afternoon.
The second-year Magpie sustained the injury in a tackle in the third quarter, with late addition Oleg Markov replacing him.
"Scans will determine how long," coach Craig McRae said post-game.
"We'll wait and see on that before making too many comments but unfortunately for the young lad he had an impact into the ground which caused the PCL (injury)."
Asked whether Sullivan could be out for the season, McRae said: "That could be a reality, but we won't know until the scans."
The 27-year-old had nine disposals and a goal assist to that point.
He has averaged 11 disposals and three tackles through 13 matches in 2025.
Markov replaced Scott Pendlebury who was a late exclusion as the Pies manage his minutes ahead of September action.
