Stone sustained a microfracture and ligament damage in his right wrist, according to the Senators, in Game 1. He was slashed by Montreal defenseman P.K. Subban.
Stone had 47 points in the last 46 games of the regular season to help the Senators reach the Stanley Cup Playoffs.
Pacioretty, who led the Canadiens in goals (37) and points (67), missed the last two games of the regular season and Game 1 of the series with an upper-body injury.
Montreal won Game 1 of the best-of-7 series 4-3.
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