Greater Western Sydney star Devon Smith will undergo surgery on his knee.
News broke earlier on Friday that Smith was withdrawn from the GWS side to take on Richmond this weekend.
Smith injured his knee during the Giants' final training session, changing direction.
GWS coach Leon Cameron revealed the injury was worse than first thought.
"He had an unfortunate accident changing direction and tweaked his knee, and has torn his meniscus," he said on Friday.
"Devon is disappointed and we're disappointed for him, because you don't expect to lose players the day before the match, but it is what it is, we move on."
He is expected to miss anywhere from six to 12 weeks.
Smith has been influential this season for the Giants, averaging 21 disposals, four inside 50s, seven score involvements and hitting the scoreboard in every game, kicking nine goals for the season.