Thornton wasn't putting much weight on his left leg after running into Canucks forward Michael Chaput with 3:05 left in the period.
Sharks coach Peter DeBoer did not have an update on Thornton after their 3-1 victory.
"We'll get home and he'll get checked out tomorrow," he said.
San Jose, which has clinched a berth in the Stanley Cup Playoffs, is four points behind the Anaheim Ducks for first place in the Pacific Division and two points behind the Edmonton Oilers for second with three games remaining.
Thornton's left knee awkwardly hit the back of Chaput's right leg as he tried to check Chaput from behind along the boards in the Vancouver zone. He went straight to the locker room, limping down the tunnel.
Thornton, 37, is fourth on the Sharks with 50 points (seven goals, 43 assists). His 1,391 NHL points are tied with Brett Hull for 22nd on the League's all-time list.
"Hopefully, he's only out short term here, but I think we're confident as a group," DeBoer said of replacing Thornton. "We're a team that's a sum of our parts, not about one or two guys. If anyone can handle it, we can."
