The Sharks, on a season-long six-game winning streak, are in second place in the Pacific Division, seven points behind the Vegas Golden Knights and four points ahead of the Anaheim Ducks.
San Jose's next game is against the Calgary Flames at SAP Center on Saturday (4 p.m. ET; NBCSCA, SNW, NHL.TV).
Thornton had 36 points (13 goals, 23 assists) in 47 games this season. He had offseason surgery on the MCL and ACL in his left knee after being injured April 2. He missed the first two games of the Western Conference First Round against the Edmonton Oilers and then returned for Games 3 through 6; the Sharks lost in six games.
"I knew what I was ahead for," Thornton told The Mercury News. "I'm really confident in my other leg, it's stronger than ever before. ... It's starting to feel normal again, which is a good sign. I still have a lot of work to do, but I'm confident I will come back healthy."
Thornton, in his 20th NHL season, ranks 16th all-time with 1,427 points (397 goals, 1,030 assists) in 1,493 games with the Sharks and Boston Bruins. He's 12th in assists, three behind Mario Lemieux.