Thornton was designated for injured reserve with an undisclosed injury Wednesday, David Dwork of Local 10 Miami reports.
Thornton sat out against the Rangers on Feb. 1 but it appeared at the time the 42-year-old center was just serving as a healthy scratch. Instead, it appears the Ontario native is dealing with a more significant injury. Considering the team can use retroactive IR and Thornton hasn't played since Jan. 31, he could be activated at any time moving forward.