Ottawa-area Liberal MP Mauril Belanger says he has been diagnosed with Amyotrophic Lateral Sclerosis, also known as Lou Gehrig's disease, and has dropped out of race to become the new Speaker of the House of Commons.

Belanger made the diagnosis public in a statement on Monday.

"Last Friday, I met with highly respected Ottawa neurologist, Dr. Pierre Bourque," Belanger wrote to his colleagues.

"After undergoing a series of tests, he has diagnosed me with Amyotrophic Lateral Sclerosis (ALS), also known as Lou Gehrig's disease. It is an incurable disease."

Prime Minister Justin Trudeau wished Belanger well Monday, with a message on his Twitter account.

"My thoughts are with my friend," Trudeau wrote.

"Stay strong. We will always have your back."

Ontario Progressive Conservative MPP Lisa McLeod also offered the Belanger family her support.

"My thoughts and prayers are with my dear friends (Mauril Belanger) and his wife (Catherine) as they deal with an ALS diagnosis. Love and hugs."

A week ago, Belanger wrote another letter, informing friends, supporters and his fellow politicians that medical tests to determine why he wasn't able to speak properly had ruled out the possibility of a stroke or cancer.

Belanger said he had experienced difficulty speaking during the final weeks of the federal election campaign.

Faced with a diagnosis of ALS, Belanger said he would not seek the Speaker's chair.

"Under the doctor's advice, I have decided to withdraw my candidacy for Speaker of the House of Commons today but shall continue as the proud member of Parliament for Ottawa-Vanier."

ALS is a progressive, neuromuscular disease "in which nerve cells die and leave voluntary muscles paralyzed," says the website for the ALS Society of Canada. It says two or three Canadians die of it every day.

It became known as Lou Gehrig's disease after it claimed the life of the legendary New York Yankees first baseman in 1941.

Brian Parsons, a former Liberal staffer on Parliament Hill, was diagnosed with a similarly aggressive form of the illness in 2013, known as Bulbar ALS, and said Belanger is facing difficult days ahead.

"Mauril has been given a death sentence and no doubt is going through hell right now, Parsons said in an email exchange with The Canadian Press.

"Speaking from experience, it's a very difficult and surreal time. You're grieving for your own death but still very much alive."

Parsons predicted that Belanger will find the inner strength to carry on for as long as he can.

"Everyone knows Mauril is a fighter, and I have no doubt he will not go down without taking a few swings at this disease."

Last year, with the help of a number of celebrities, the "Ice Bucket Challenge" campaign turned into a social media sensation, helping to raise awareness of the disease, along with millions of dollars for research.

Belanger had been considered a top contender for the Speaker's job.

He was first elected as an MP in a 1995 by-election and has held his seat ever since. He was named to several junior cabinet posts in the Paul Martin government.

Fellow Liberal MPs Geoff Regan, Denis Paradis, Scott Simms and Yasmin Ratansi have also expressed an interested in running for the position, along with Conservative Bruce Stanton.

Rookie Winnipeg Liberal MP Robert-Falcon Ouellette had also put his name forward, but withdrew over the weekend after controversial remarks he made about the position.

Electing the Speaker is the first order of business in the Commons once the 42nd session of Parliament begins on Thursday and must be done before the speech from the throne can be read the next day.

Conservative MP Andrew Scheer, Speaker in the last Parliament, has said he will not run this time around and has been named Conservative House leader.