Ben Sinclair will play no further part in the AFL season as Collingwood assess his fourth concussion of the year.
Sinclair was knocked out on July 22 in the opening quarter of the Magpies’ clash with North Melbourne at Etihad Stadium.
The 24-year-old was taken to hospital for precautionary scans but cleared of serious damage.
Sinclair trained the following week but was left on the sidelines for Collingwood’s matches against West Coast, Richmond and Western Bulldogs.
The club announced on Monday the defender would also miss the final two rounds of the season.
“We need to get to the bottom of it and give him a decent chance to be able to put some games together,” Magpies football manager Neil Balme told the club website.
“He’s very keen to play, as we are.
“But naturally there’ll be quite a bit of testing that he’s got to go through to make sure he’s OK.
“Another thing we’ll have to look at is how this keeps happening to him.”
Sinclair also suffered head knocks in rounds four and six, while a knock at training in May made it three concussions in the space of a month.
Recent research has highlighted the risks of long-term damage resulting from repeated knocks to the head.
Adelaide’s Scott Stevens, North Melbourne forward Leigh Adams, Geelong’s Sam Blease and Brisbane Lions Jonathan Brown, Matt McGuire and Justin Clarke are among the players to recently retire because of concussion concerns.
Clarke retired earlier this year after being crunched in a marking contest at training.
The 22-year-old suffered dizziness, severe headaches and memory loss.
Sinclair’s condition is nowhere near as serious, and Balme said he had “recovered quite well” from his latest concussion.
“He’s training but we don’t think we’ll take a risk for the rest of the year,” Balme said.
Balme also confirmed midfielder Taylor Adams (ankle) and key defender Ben Reid (knee) would also miss the rest of the season.
The Magpies are unsure whether veteran defender Reid will require surgery.