The 30-year-old injured his hamstring tendon in the club's opening round NAB Cup match against Geelong, and was initially expected to miss up to eight weeks.
The ruckman has since aggravated the injury, and it's now uncertain when he will make a return.
Fremantle football operations manager Chris Bond said Sandilands will seek further advice.
"Once Aaron has been assessed by the specialist and we have his medical report, we will be in a position to comment further on the preferred course of action," Bond told fremantlefc.com.au.
Fellow ruckman Zac Clarke failed to complete training on Tuesday, but the club insists he has escaped serious injury, and could yet line up for round one.
Jacqui Reed is a reporter for AFL.com.au. Follow her on Twitter @JacquiReedAFL
