Carlton spearhead Levi Casboult has suffered what may be a serious knee injury early in the AFL clash with Port Adelaide.

The 26-year-old forward marked strongly in a contest with Power marker Tom Jonas but his knee buckled in the tangle of legs with his opponent.

Casboult couldn’t get up after tumbling to the ground, grimacing and calling for assistance.

He was ushered straight down the race and into the Carlton rooms, with reports suggesting he had injured both his knee and ankle.

Sports doctor Peter Larkins suggested a possible season-ending ACL injury might have occurred, tweeting “Levi Casboult in trouble after left knee hyperextension – blues will check ACL & lateral capsule – doesn’t look good”.

Casboult, who is uncontracted at season’s end, was sighted with ice on his left knee, suggesting his day was done and the potential for serious injury.