Although scans cleared him of any damage to his spine, he was unable to return to training after repeatedly failing concussion tests.

If he does retire, Clarke would become the third Lion to have his career cut short by concussion, following the retirements of Jonathan Brown and Matt Maguire.

Clarke has played 56 games as a key defender in his three-year career, and has been seen as one of the club's bright prospects for the next decade.

He is also one of the more academically gifted players in the AFL and is studying engineering after scoring 99.95 on his Australian Tertiary Admission Rank entrance score.

He also has a pilot's licence. His interests outside football are said to play a big part in his decision as he considers his prospects beyond the game.