No surgery will be required, however, the club announced on Tuesday that the three-time All Australian will be sidelined for up to eight weeks.
It continues a frustrating run of injuries for the AFL's tallest player, who has been restricted to 27 games in the last two seasons because of a recurring toe injury.
Fremantle was initially hopeful that Sandilands had only suffered buttock tightness on Saturday night, but the ruckman remained at the club to be assessed as Fremantle travelled to Jurien Bay and Dongara for its community camp.
The club will likely call on Jon Griffin to lead the ruck in the early rounds, with support from Zac Clarke, who has impressed in his fourth pre-season and added 5kg to his frame.
"It's certainly unfortunate that Aaron will be out for an extended period of time, but we have great confidence in our structures and players to be able to fill the role," football manager Chris Bond said.
Griffin played 13 games last season and proved he could lead the ruck in Sandilands' absence, averaging 24.7 hit-outs.
The club also added to its ruck depth at last year's NAB AFL Pre-Season Draft, recruiting 21-year-old ruckman Jack Hannath from SANFL club Central Districts.
Griffin and Hannath both played in Fremantle's opening NAB Cup matches, but Clarke was rested after suffering an adductor tweak.
Coach Ross Lyon said Clarke would be available during the NAB Cup.
Nathan Schmook is a reporter for AFL Media. Follow him on Twitter: @AFL_Nathan
