The forward and former Canadiens captain has two goals in 12 games for Vegas, which acquired him in a trade with Montreal for forward Tomas Tatar, forward prospect Nick Suzuki and a second-round pick in the 2019 NHL Draft.
Pacioretty had five 30-goal seasons and 448 points (226 goals, 222 assists) in 626 games through 10 seasons with the Canadiens from 2008-18.
Vegas, which is 3-4-1 in its past eight games, will look for its third win in four games.
Goalie Antti Niemi will make his fifth start for Montreal, which has lost consecutive games for the first time this season. He is 3-1-0 with a 3.13 goals-against-average and .893 save percentage.