Horton had a concussion during the Stanley Cup finals against Vancouver last year. He played in 46 games this year before sustaining another one Jan. 22 against the Philadelphia Flyers.
Chiarelli says goaltender Tuukka Rask is a little "better" than day to day. The backup has been out since March 3, when he strained a muscle in his groin and lower abdomen.
The defending Stanley Cup champions begin their title defense against the Washington Capitals.