Scans have confirmed that retiring Richmond forward Chris Knights will need a knee reconstruction after tearing his anterior cruciate ligament at training on Thursday.

Knights, 28, injured his left knee in an innocuous tackle during the session at Punt Road and had to be helped from the ground by trainers.

He was sent for scans, which confirmed the extent of the injury.

A photograph of a player being carried from the field circulated on social media on Thursday morning, with a suggestion it was captain Trent Cotchin.

But it was confirmed to be the desperately unlucky Knights, who had kept training with the Tigers after announcing his impending retirement last month in the hope of an unlikely finals call up.

It's the other knee to the one that dramatically collapsed on him in round seven, 2013, in just his fifth game as a Tiger.

From that day on, the former Crow has battled problems with the knee and soft tissue injuries, and has only been able to play one AFL game since.

Knights made his AFL return in round three this season against the Brisbane Lions but broke down with a hamstring injury that needed surgery and cost him 10 weeks.

He has been in and out of the VFL since, with a quad injury interrupting his ability to string games together.

Knights played 96 games for the Crows before returning to his home state of Victoria to play for the Tigers.

Knights was emotional when he told his teammates of his decision to retire two weeks ago, and spoke of how grateful he was for the support and care he was given throughout his difficult time as a Tiger.

"It's been a tough three years here, and no doubt you guys are aware with

"I couldn't have got through it without the help of everyone in this room, especially the players and the support staff."