MONTREAL -- A situation that has been brewing all season came to a head Tuesday with Montreal Canadiens coach Michel Therrien making center David Desharnais a healthy scratch for their game against the St. Louis Blues.

Desharnais has one assist in 15 games this season, and dating back to last season he has one goal and eight assists in his past 32 regular season and Stanley Cup Playoff games.

"It's never easy to make a decision like this," Therrien said. "The principle is to always make it so a player is at his best, but when we don't see results decisions need to be made."

Desharnais, 27, is in the first of a four-year, $14 million contract he signed in March, one he earned with a 60-point season in 2011-12. But last season was a down year for him with 28 points in 48 games, and he is in the midst of the worst slump of his NHL career.

"This is a challenge for him," Therrien said. "It's up to him now to react well, and we expect him to do that."

Desharnais' spot will be filled by American Hockey League veteran Martin St. Pierre, who will play his first game in a Canadiens uniform. Though St-Pierre, 30, has played 38 NHL games, this one will be extra special for the Ottawa native.

"I'm nervous even if it's my 10th year [of professional hockey]," St. Pierre said. "But I can convert that nervousness into motivation."

The Blues will also have a subtle change to their lineup, with coach Ken Hitchcock juggling his lines to create more balance offensively.

The top line of Alexander Steen, David Backes and T.J. Oshie has dominated the Blues' offense this season with 20 of the team's 43 goals. Oshie, who has two of those goals, will play with Derek Roy and Vladimir Sobotka while Chris Stewart takes his spot on the big line.

"We just need more participation," Hitchcock said. "We're going to include more guys in having success, and for us to get to the next level we need more participation. We need more people doing more things.

"I guess the best way to describe it is we need more followers. If we get more followers I think we'll be in really good shape. We have great leadership and performance from certain guys, but we need a closer following group for us to have long-term success."

The goaltending matchup pits Montreal's Carey Price against Jaroslav Halak for the Blues, their third showdown since Halak was traded to the Blues by the Canadiens in order to allow Price to become the undisputed No. 1 in Montreal in the summer of 2010.

Halak has won both the previous meetings, stopping 46 of 47 shots and holding a shutout streak of 107:30 against his former team going into the game Tuesday.

Here is what the lineups should look like for the Blues and Canadiens:

BLUES

Alexander Steen – David Backes – Chris Stewart

Derek Roy – Vladimir Sobotka – T.J. Oshie

Jaden Schwartz – Patrik Berglund – Vladimir Tarasenko

Ryan Reaves – Maxim Lapierre – Adam Cracknell

Jay Bouwmeester – Alex Pietrangelo

Barret Jackman – Kevin Shattenkirk

Jordan Leopold – Roman Polak

Jaroslav Halak

Brian Elliott

Scratched: Chris Porter, Ian Cole

Injured: Brenden Morrow (upper body), Magnus Paajarvi (upper body)

CANADIENS

Max Pacioretty – Alex Galchenyuk – Brendan Gallagher

Michael Bournival – Tomas Plekanec – Brian Gionta

Rene Bourque – Lars Eller – Louis Leblanc

Martin St. Pierre – Ryan White – George Parros

Andrei Markov – P.K. Subban

Josh Gorges – Raphael Diaz

Douglas Murray – Francis Bouillon

Carey Price

Peter Budaj

Scratched: David Desharnais, Greg Pateryn

Injured: Daniel Briere (concussion), Brandon Prust (shoulder), Alexei Emelin (knee), Davis Drewiske (shoulder), Travis Moen (face)