Mundy landed awkwardly on his right leg on the half forward flank of Patersons Stadium just 10 minutes into the game on Sunday and immediately knew that he was in trouble.
Fremantle medical staff reported after the match that Mundy had suffered a possible fractured fibula.
The 25-year-old was helped from the ground and was unable to put any weight on his leg.
Mundy was immediately handed the red substitute vest, with Clayton Hinkley coming on to play his first game of the season.
The midfielder hobbled down into the rooms on crutches shortly after with ice applied just below his right knee.
Mundy had a standout 2010 season, averaging 22 possessions a game and winning the Doig Medal in a team that made it to the second week of the finals, and has continued on strongly this year averaging 29 disposals per match.
