The 40-year-old told reporters during the NHL Awards in June that he planned to return for the 2019-20 campaign, and, according to The Athletic's Kevin Kurz, there is "no doubt" Thornton will re-sign with the Sharks in the near future.
Teammate Timo Meier also feels confident about the future Hall of Famer's return to the Bay Area.
"I think everybody that knows 'Jumbo' expects him to be back," Meier said according to NHL.com's Dan Rosen.
"The way he's training and the way he's still in shape with his 40 years, I don't doubt that he's coming back. He'll be playing until he can't anymore. Probably he'll play longer than he can walk. I really hope he's going to be back because he's just a huge presence and the guys all love him there and obviously we all know what kind of hockey player he is."
Thornton has spent 14 seasons with the Sharks, playing each of the previous two campaigns on one-year deals. The former Hart Trophy winner is the franchise's all-time leader in assists and ranks second in both games played and points.
The Sharks have $4.68 million in projected cap space with a roster of 21, including 11 forwards, according to CapFriendly.