Couture has been out since he was hit in the face with a puck -- knocking out several teeth -- in Nashville on March 25. Thornton hurt his left knee on Sunday in Vancouver.
Coach Peter DeBoer expects both players back eventually, but he said they are listed as day-to-day until they return. DeBoer said he has no time frame for when that will be.
Couture has 25 goals and 27 assists. Thornton has seven goals and 43 assists.
The Sharks have clinched a playoff spot and are playing for positioning in the final three games of the regular season.