The Dallas Stars fired second-year coach Jim Montgomery on Tuesday for what the team called unprofessional conduct.
General Manager Jim Nill said Montgomery had acted inconsistently with "core values and beliefs of the Dallas Stars and the National Hockey League."
He did not elaborate.
Nill said he became aware Sunday of an act by Montgomery and the decision to fire him came after an internal investigation that included discussions with the team's general counsel.
Nill said only that it was not because of a criminal act, had no connection to players, past or present, and didn't involve another employee of the team.
Nill, who hired Montgomery, called the incident a "total surprise."
Rick Bowness, who came on an assistant coach with Montgomery, was named interim head coach for the rest of the season.
Four NHL coaches have lost their jobs this season, three of them amid allegations of misbehavior.