Sainsbury tore a pec muscle after a "freak" gym incident in the weeks leading up to their Friday night grand final rematch at Industree Group Stadium and is expected to be ruled out for the rest of the year.
The centre-back has only played one game for the Mariners so far, featuring in their 3-1 AFC Champions League Elite defeat to Shandong Taishan, after joining Mark Jackson's side in August on a three-year deal.
Sainsbury returned to the club that launched his career after a 10-year career overseas, most notably in the Netherlands, and had played 60 games for the Mariners between 2010 and 2014.
Trent Sainsbury wins a header during a Mariners-Glory clash in 2012. (Paul Miller/AAP PHOTOS)
"Trent's going to be out until the new year so it's a big, big blow for him and for us in particular," Jackson said on Friday.
"It was a freak incident in the gym. He tore a pec muscle. It was nothing which any of the staff or him could have done different.
"We're going to miss his leadership on the pitch, but off the pitch, he's still there."
Jackson says highly-rated defender Brian Kaltak will fill in as captain, as his new-look side begin their championship and premiership defence after losing several key players in the off-season.
Josh Nisbet, Max Balard, Jacob Farrell and the retired Danny Vukovic were among the departures for the club, who are also looking to defend their AFC Cup title.
"Everybody wants to achieve the ultimate goal at the end of the season. That's what you set out to do," Jackson said.
"All we try and do is, particularly with such a turnover of players and losing key players and trying to replace them, is we try and embed the new players into our culture of a club, our way of playing.
"I think it'll take time again this year but I really have a good feeling about the players, particularly in this week leading up to this game, that they feel ready and prepared and hungry to get going."
First-year Victory coach Patrick Kisnorbo expects a full roster to be available for selection bar a suspended Daniel Arzani, with Socceroos pair Jason Geria and Nishan Velupillay set to play fresh from their World Cup qualifier in Japan.
The Victory will be looking for redemption after coughing up a 1-0 lead in the 91st minute to lose last season's grand final in their last meeting with the Mariners.
Brian Kaltak celebrates after Ryan Edmondson's dramatic late grand final goal. (Dan Himbrechts/AAP PHOTOS)
A fantastic Geria strike had put Victory ahead for 90 minutes before substitute Ryan Edmondson popped up to level and set up a 3-1 win in extra time.
On Saturday, new ALM club Auckland FC will host Brisbane Roar and Newcastle play Melbourne City before Western Sydney and Sydney FC show off respective marquee signings Juan Mata and Douglas Costa at CommBank Stadium.
Wellington Phoenix kick things off on Sunday against Western United and Australia Cup champions Macarthur FC take on Perth Glory to close out the first round.
Adelaide United have a bye.
