Referee Wes McCauley was forced to exit Game 6 between the St. Louis Blues and San Jose Sharks in the first period after colliding with linesman Scott Cherry during play.
Gord Dwyer replaced the official, and the NHL later announced McCauley will not return.
Sportsnet's Scott Oake said on the broadcast that McCauley told him it's a hamstring injury.
The veteran referee is the most popular official in the league, and one of the most well respected.
He'll likely be in line to work the Stanley Cup Final if healthy.
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