SAM LONERGAN has joined Orren Stephenson and Ricky Petterd as mature-age Richmond rookies eligible for the AFL after being promoted to the senior list.

The former Essendon midfielder was elevated on Thursday in place of the injured Chris Knights.

Knights will miss the rest of the season after dislocating his kneecap and rupturing his patella tendon against Port Adelaide on Saturday at AAMI Stadium.

He had surgery on Sunday after the team returned to Melbourne.  

Lonergan, 26, had an interrupted pre-season after ankle surgery last year and started the VFL season late after hamstring problems.  

He has recovered to play well in the two games he has managed in the VFL.  

Lonergan played 79 matches with the Bombers after being recruited in the 2005 NAB AFL Draft.

Former Geelong ruckman Stephenson played his first game for the club last week against the Power, while Petterd has played five but is sidelined with a calf injury.

The ex-Demon is expected to be available next week.

Jennifer Phelan is a reporter for AFL Media. Follow her on Twitter @AFL_JenPhelan.