"I want to be with my teammates competing, but at this moment there are things more important than hockey in my life, and that is being with my family," the star netminder said in a statement.
"I want to thank the Bruins and my teammates for their support and wish them success," he added.
Shortly thereafter, Bruins general manager Don Sweeney implied he wasn't blindsided.
"I don't think it's any big surprise to us. ... This has been a difficult decision for Tuukka, but the Boston Bruins are in full support of why he made this decision," the GM told reporters on Saturday.
Sweeney added: "I think we all understand that these are trying times for everybody. The NHL's done a fabulous job of protecting the players' health and safety, but the priority for Tuukka at this point in time, rightfully so, has to be his family, and we support that."
The GM also confirmed Rask's family is healthy and said the goalie's decision isn't related to any specific issue.
The Carolina Hurricanes - who are facing the Bruins in the opening round of the playoffs - offered well wishes before Game 3 on Saturday afternoon.
Rask is a finalist for the Vezina Trophy this season after winning the award in 2014. The veteran puck-stopper helped the Bruins win the Presidents' Trophy in 2019-20, posting a .929 save percentage - which led the NHL among goalies who played more than 30 games - and five shutouts in 41 contests, all of which were starts.
His wife recently gave birth to the couple's third child.