Sandilands met with prominent surgeon Dr Julian Feller in Melbourne late on Monday afternoon to determine what course of recovery was necessary.
After that consultation the club announced that surgery was the best option available to repair the injury.
Fremantle's general manager of football operations Chris Bond said that although the news was very disappointing for the 30-year-old, it was possible that with an appropriate period of recovery and structured rehabilitation he could be available for selection midway through the season.
However until surgery took place Bond said it was difficult to name a likely return date for the three-time All Australian.
"At this stage we will have to wait until after his surgery and the recovery phase before we can be more specific about when Aaron will be available for selection," Bond said.
Sandilands hurt his left hamstring in round one of the NAB Cup. He has battled injury for the past two seasons playing 27 of a possible 46 games.
Speaking on radio 6PR after hearing the news Fremantle coach Ross Lyon was upbeat and said the prognosis was that the injury was the minor end of the scale.
Lyon said Sandilands had a slight split in the tendon and his injury was not the same as a more severe hamstring injury suffered by Saints skipper Nick Riewoldt in 2010.
"We think it's more likely eight weeks [on the sidelines] unless they got in there and it was something different to what they were thinking, but that is highly unlikely so it's really at the minor end," Lyon said.
"[There's] been a lot of doomsayers out there saying it is the end of his career … this is quite minor and he'll be able to condition really well and play a huge part for us."
Sandilands was All Australian between 2008-2010 and won the club best and fairest in 2009.
In 2012, Sandilands was injured in round 11 and missed rounds 13-20. He returned in round 21 from a toe injury and played the last five games of the year, which included two finals.
