Carlton and West Coast were forced to activate their subs midway through the second term in today's clash at the SCG.
Leading goalkicker Harry McKay and Eagles defender Brad Sheppard were the two players subbed out of the game, both sustaining concussions in separate incidents in the first term.
McKay hit his head on the turf after coming off second best in a marking contest, while Sheppard collided heads with Adam Saad.
McKay was replaced by medical sub, Jack Newnes, while Jamaine Jones entered the game for Sheppard.
Sheppard will miss next Sunday's clash against Richmond because of the 12-day concussion protocols, while McKay will hope to be fit to face GWS in Round 14.