Josh Begley's AFL season is over with scans confirming the Essendon forward has a torn anterior cruciate ligament.
The 19-year-old twisted his right knee in the first quarter of the Bombers' 49-point Anzac Day loss to Collingwood. He will undergo a reconstruction next week.
"We are all disappointed for him," Essendon football boss Dan Richardson said on Thursday.
"He has made a really promising start to his career, including playing every game this season.
"Importantly, he has great support around him, he is a terrific young man and we are confident he will make a full recovery following a successful rehabilitation program."
Forward partner Josh Green is facing several weeks on the sidelines after suffering a right hamstring strain during the Anzac Day clash.
With just four days to prepare for Sunday's match against Melbourne at Etihad Stadium, the Bombers have also ruled out goalsneak Orazio Fantasia (groin) for another week.
Essendon's poor Anzac Day performance cancelled any gains from their upset round-four win over Port Adelaide and left them in 13th place with a 2-3 record.