The 61-time Socceroo watched from the sidelines as the Mariners scored their first win of the new campaign on Friday night, a 2-1 come-from-behind victory over rivals Newcastle Jets in Unite Round.
But Sainsbury is "absolutely flying" in his recovery from the pectoral injury that has delayed his return to the Mariners, the club where he made his professional debut as a teenager in 2010.
The 32-year-old defender has not set a date for his first Mariners appearance since 2014, but feels confident it is fast approaching.
"I'm absolutely flying," the new Mariners captain told AAP.
"The injury, I'm taking it one day at a time, I'm healing well, healing fast so I'm on track to come back soon.
"The confidence is always going to be high no matter what, even if I'm injured. I could strap myself up and go out there with one arm. I believe in my ability, so coming back I don't think is going to be an issue."
Sainsbury worked across the world in a decade out of the A-League, notably becoming only the ninth Australian to play in Italy's Serie A while on loan to Inter Milan from Jiangsu Suning in 2017.
During his time with the Netherlands-based PEC Zwolle, Sainsbury won the Dutch Cup and the Dutch Super Cup, and later played club football in Qatar, Israel and Belgium.
A return to Australia had always been on Sainsbury's mind during his stint abroad, but he wanted to make the shift sooner rather than later.
"I wanted to come back to Australia and I didn't want to come back as the old basket case, I wanted to come back with fight in the belly," said Sainsbury, in the first season of a three-year deal.
"The body's in good shape, obviously with the injury to the pec it's going to take a little bit longer but I've come back with a lot still to achieve in the A-League."
During his injury, Sainsbury has enjoyed mentoring the next generation of Mariners, some of whom were toddlers during his first stay at the club.
He singled out 16-year-old midfielder Haine Eames as a player of particular promise.
"I was playing in the A-League when he was one year old. He's a young pup, a young kid but he's got a very big future ahead of him," he said.
His leadership role has helped Sainsbury avoid feeling like the "old basket case."
"It's keeping me young and fresh. I feel like a 22-year-old again amongst the boys," he said.
