Former prime minister Jean Chretien is recovering in a Montreal hospital after undergoing surgery to relieve a potentially life-threatening pooling of blood on his brain.

Doctors at Montreal's Jewish General Hospital said Chretien had surgery to relieve a spontaneous subdural hematoma, or a collection of blood between the skull and the brain, on Friday afternoon.

Neurosurgeon Dr. Jeff D. Golan performed the two-hour surgery immediately after a CAT scan showed the three-centimetre hematoma on the right side of Chretien's head.

"I believe we intervened at the appropriate time," Golan told reporters on Saturday during a news conference at the hospital. "His symptoms were slightly getting worse and by the time that I saw him I felt that it was necessary to intervene immediately."

Doctors said they received a phone call from Chretien's daughter on Thursday and she reported her father had been having difficulty walking for several days. His condition had worsened over the previous couple of days and he was experiencing some weakness on his left side.

Chretien arrived at the hospital around 9:30 Friday morning and underwent a series of tests. The CAT scan showed the hematoma, but even more troubling, that it was displacing his brain by about 1.5 cm. This put Chretien at risk of a stroke.

Golan said the surgery involved opening the skull to gain access to the subdural cavity, or the region between the skull and the brain, and then removing the accumulated blood and blood products that were pressing on the brain.

Golan said Chretien has not suffered any adverse effects from the operation and will fully recover within two to four weeks.

"Naturally we're going to keep him under observation for another two, three days, but his otherwise hectic lifestyle will have to wait for a few weeks," Golan said. "He's going to have to rest and avoid some of his otherwise regular activities."

Bleeding likely present for weeks

Golan said there is no way to tell exactly what caused the hematoma. But Chretien's daughter did report that her father had hit his head in his home's basement staircase sometime near the end of June.

"Often in such situations we don't know why or what was the cause," Golan said.

"In this situation it seemed like the bleeding was present in some shape or form for at least a week or two."

Chretien appeared in good health when he attended the unveiling of his official portrait on Parliament Hill in late May.

In a statement issued Saturday, current Liberal Leader Michael Ignatieff said Chretien was in fine spirits when the he saw the former prime minister in his hometown of Shawinigan just two weeks ago.

"He was his usual self, with that spring in his stride of a man half his age and all the strength, vigor and sense of humour Canadians had come to see in him over the decade he served as one of our greatest Prime Ministers," Ignatieff wrote.

"I am greatly relieved to hear that his ailment was given immediate attention and that he and his family can expect him to be fully recovered soon."

In his own statement, Prime Minister Stephen Harper echoed that confidence in a "speedy and full recovery."

"Mr. Chretien, I am sure, will emerge as he always has from every challenge, by winning," Harper said.

Chretien, 76, served as an MP for 40 years and led three Liberal-majority governments in a decade as prime minister.

Chretien left public life when he resigned as prime minister in December 2003, and went to work for Heenan Blaikie, mostly at the law firm's Ottawa office. But he is also active at the Montreal office, according to the firm's website.

He underwent emergency quadruple bypass surgery in 2007 at the Montreal Heart Institute, shortly before his memoirs were published.