Montreal Canadiens great Jean Beliveau suffered a stroke late Monday and was in stable condition in hospital, the Habs announced Tuesday.
Beliveau, 80, was undergoing tests and treatment and remained under observation at Montreal General Hospital.
Former Canadiens coach Jean Perron said the Hall of Famer's health had deteriorated during the past few months. Beliveau's wife of 59 years, Elise, also had had a stroke in recent months but has recovered.
Politicians and fans from across the country sent well-wishes to Beliveau, long considered one of the game's classiest gentlemen.
"Mr. Beliveau is a great Canadian and a remarkable ambassador for our national sport," Prime Minister Stephen Harper said in a statement. "We wish him a speedy recovery."
Colorado Avalanche forward Matt Duchene, 21, tweeted: "Thoughts and prayers going out to Jean Beliveau and his family. One of the greatest and a hero of mine."
Beliveau, a former Canadiens captain and a 10-time Stanley Cup winner, has had health issues over the years. He needed surgery last June because of abdominal aneurysms.
In January 2010, he also had a stroke. He spent 18 days in hospital and doctors replaced his pacemaker, which had been installed in 1996.
The native of Trois Rivieres, Que., needed radiation treatment in 2000 when a cancerous tumour was discovered in his neck.
During his career with the Canadiens, Beliveau had 507 goals and 712 assists in 1,125 regular-season games, along with 79 goals and 97 assists in 162 playoff games.
He joined the Canadiens for a handful of games during the early 1950s, becoming a fixture with the team from the 1953-54 season until retiring in 1971. He then moved into a front-office position with the Canadiens and had his name inscribed on the Stanley Cup a further seven times as an executive.
Among his many honours, Beliveau was a six-time first-team all-star; twice won the Hart Memorial Trophy as NHL MVP (1956, 1964); and was the inaugural winner in 1965 of the Conn Smythe Trophy as playoff MVP.
He was inducted into the Hockey Hall of Fame in 1972 and was made a Companion of the Order of Canada in 1998.
The Canadiens said Beliveau's family has requested privacy.