The three-time All Australian initially hurt his left hamstring during Freo’s opening NAB Cup hitout in February.
After aggravating the injury recently, Sandilands will now undergo surgery and miss between 8-12 weeks of football.
But Lyon said his star ruckman’s injury was not as severe as the one Nick Riewoldt suffered in 2010 that forced the St Kilda forward to miss 11 games.
"We think it's more likely eight weeks, unless they (the surgeon) 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 on 6PR last night.
The Freo coach was confident Sandilands would be back playing at his best again in 2013.
“There have 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 in three consecutive years from 2008-2010 and won the Doig Medal in 2009.
