The Canadiens had indicated Price was unlikely to be ready for the season opener against the Toronto Maple Leafs on Oct. 13. Coach Dominique Ducharme said Wednesday that Price was "not doing well right now."
Ducharme said the expectation was to ease Price back into the lineup after the star goalie had offseason surgery to repair a torn meniscus.
Canadiens general manager Marc Bergevin said that he learned of Price's decision Wednesday and that "the news caught me off guard." The GM addressed the team Thursday morning. Bergevin said that Price will be away from the team for a minimum of 30 days but that it "could be longer." He said he believes Price will be back with the team this season.
The NHL and NHLPA jointly announced Price's decision and said there will be no further comment.
Angela Price, the goaltender's wife, posted a message on Instagram after the announcement.
"Part of the privilege of being in the position our family is in, is that we also get a public platform to show how there is and can be a path to light for anyone who is struggling. No matter what is on the line, we hope we can communicate the importance of putting your mental health first not just by saying it, but by showing up and doing the work to get better," she wrote.
"Carey's showing up for himself and our family and making the absolute best decision possible for us. I will continue to show up for him and our kids and seek out the support I may need on any given day."
Price, 34, is entering his 15th NHL season, all with Montreal. He's on the fourth year of an eight-year, $84 million contract. He was a primary factor in the Canadiens' surprising run to the Stanley Cup Final last season, posting a .924 save percentage. Price is a two-time Vezina Trophy finalist as the league's top goaltender, winning that award, as well as the Hart Trophy for NHL MVP, in the 2014-15 season.
The Canadiens will rely on Jake Allen, 31, who was Price's backup and appeared in 29 games last season. He was formerly a starting goalie for the St. Louis Blues. They claimed goalie Samuel Montembeault on waivers from the Florida Panthers on Saturday.