The Boston Bruins say Horton is considered "day-to-day" after he appeared to suffer an upper-body injury last night in a 4-3 triple-overtime loss to the Chicago Blackhawks.
Bruins coach Claude Julien declined to give more details on Horton, and he would not reveal who would take the forward's place in the lineup. Jordan Caron and Jay Pandolfo appear to be the most realistic options.
Julien said every extra player was ready to step in if necessary.
Horton has seven goals and 11 assists in the playoffs skating on the Bruins' top line with David Krejci and Milan Lucic.
Tyler Seguin took Horton's place on the top unit in Game 1. Julien was pleased with Seguin's performance but said he has to finish better on his chances.