Adelaide star Brodie Smith has ruptured his anterior cruciate ligament and will miss the rest of the AFL finals series and a big chunk of next season.
Smith left Thursday night's 36-point qualifying final win over Greater Western Sydney in the first quarter and did not return.
His right knee buckled under him as he attempted to tackle the Giants' Josh Kelly on the members' wing at Adelaide Oval, with scans on Friday morning confirming the worst-case scenario.
"The injury is really disappointing for both Brodie and the club as we start our finals campaign," Crows football chief Brett Burton said.
"We will consult a specialist this week with the view to Brodie having surgery, which will unfortunately rule him out for the season.
"Brodie will still be an important part of the group as we continue through September."
A dejected Smith clearly feared the worst after the incident and was comforted by assistant coach James Podsiadly during the quarter-time break.
The 25-year-old will miss 10-12 months if he undergoes a traditional knee reconstruction.
But he could feature next season if he opts to have an artificial ligament replacement via LARS surgery.
Smith will be sorely missed by the Crows, who earned another week off and set up a home preliminary final with the dominant win over the Giants.
The damaging half-back flanker played all 22 home-and-away games in 2017, kicking 11 goals and averaging 21 disposals.
"He is clearly pretty shattered and we're shattered for him," Adelaide coach Don Pyke said.
"He has put a lot of energy and heart and soul into the season."
Crows vice-captain Rory Sloane will return from appendix surgery for their home preliminary final in a fortnight.