Philadelphia general manager Paul Holmgren made the announcement through a team spokesman early in the first period of the Flyers' 4-3 victory in Montreal on Thursday night.
"It's really tough news about Chris," said coach Peter Laviolette, who learned the news just before the game. "I think first and foremost we wish for him to have good health and anything after that I guess we'll sort it out."
Pronger has been sidelined since Nov. 19.
"After consultation with respected concussion specialists Dr. Joseph Maroon and Dr. Micky Collins, it is the opinion of both doctors that Chris is suffering from severe post-concussion syndrome," Holmgren said. "It is the recommendation of doctors Maroon and Collins that Chris not return for the remainder of the 2011-12 season or playoffs. Chris will continue to receive treatment and therapy with the hope that he can get better."
Pronger visited Maroon and Collins on Wednesday in Pittsburgh after complaining about a fairly persistent headache and sluggish feeling. The 37-year-old defenseman also missed six games this season because of an eye injury, and had surgery on his left knee last month.
"It's hard to replace a guy like that," Laviolette said. "He plays 26, 27 minutes and there's no one individual in the organization that we can find somewhere and replace him."
In 13 games this season, Pronger had a goal and 11 assists. He has 157 goals and 541 assists in 1,167 career regular-season games in 18 seasons with Hartford, St. Louis, Edmonton, Anaheim and Philadelphia.
The 6-foot-6 player led Anaheim to the 2007 Stanley Cup title and won Olympic gold medals with Canada in 2002 and 2010. He signed a seven-year contract with Philadelphia in 2009.
"You can't replace the kind of guy he is," said Andrej Meszaros, who was among the many Flyers players who learned the news about Pronger from reporters after the game. "I hope he's going to be healthy as soon as possible and we'll have to find a way to win games without him. We've done a pretty good job so far but that's a tough break."
Flyers star forward Claude Giroux, the NHL scoring leader with 39 points, also is out indefinitely with a concussion. He took an inadvertent knee to the head from teammate Wayne Simmonds in a game Saturday.
"Claude's status remains the same," Holmgren said "He is out indefinitely."