Carlton forward Jarrod Pickett has ruptured the patella tendon in his right knee at training.
Pickett went down after a collision at training on Thursday morning, immediately going for scans.
The scans confirmed the 22-year-old has a ruptured patella tendon, which will require surgery on Friday.
There is no current timeframe on his return.
Carlton head of football Brad Lloyd said Pickett had the club's full support as he looks to begin his recovery.
“Our whole club feels for Jarrod who has worked so hard to get himself back into our AFL program over the last month,” he said.
“While the news is disappointing, as a club we will be there with Jarrod through every stage of his recovery and ensure he gets back out on the field in navy blue.
“Our playing group is very resilient and take every challenge in their stride. This challenge now presents an opportunity for a younger player to step up and seize their opportunity.”