TORONTO (Reuters) - Toronto Mayor Rob Ford, who gained global notoriety for admitting he smoked crack cocaine, dropped his re-election bid on Friday, citing a health crisis, but his older brother took his place in the race to run Canada's largest city.

In drama worthy of Shakespeare, the family switch was made minutes before a deadline for changes to the city election ballot, which also saw a Ford nephew withdraw to allow his uncle, the mayor, to run for a city council seat in his place.

Mr Doug Ford, the mayor's older brother and campaign manager, is regarded as less charismatic but less volatile than his larger-than-life sibling, who steadfastly refused to resign even as he admitted buying illegal drugs while in office and checked himself into rehab. "My heart is heavy when I tell you I am unable to continue my campaign for re-election as your mayor," Mr Rob Ford said in a statement, adding that he could be "facing the battle of my lifetime". "I've asked Doug to finish what we started together so that all we've accomplished isn't washed away. I've asked Doug to run to become the next mayor of Toronto because we need him."

The 45-year-old mayor was hospitalised on Wednesday after complaining of unbearable abdominal pains and was diagnosed with a tumour. He is undergoing a battery of tests, with biopsy results expected in a week.

The Oct 27 election is seen as a referendum on Mr Ford's four tumultuous years leading Toronto. Recent polls had shown him in second place in a tight three-way race for mayor of Canada's financial capital and largest city with a population of six million.

At a press conference on Friday evening, an emotional Doug Ford said that it had been a difficult few days for his "close-knit" family and in particular for his brother, who did not take the decision to step down from the mayoral race lightly.

"This is more than a job for Rob, it's his life's work and his passion to fight for this city, and for each and every one you," Mr Doug Ford told reporters and supporters gathered outside his mother's home in suburban Toronto. "He told me that he needed me to take the torch while he focuses on getting better."

A 49-year-old businessman, Mr Doug Ford was elected as a city councillor in 2010 when his younger brother became mayor.

"He's a Machiavellian figure and he's been called many things but not necessarily a gifted politician or someone with the gift of charisma," Professor Phil Triadafilopoulos, a political science professor at the University of Toronto, said before Mr Doug Ford's nomination for mayor was filed.

"The question is whether, if there is a welling of sympathy, if it goes over and helps a potential Doug Ford candidacy so that he can survive his innate lack of charisma... by taking advantage of the sympathy that people are feeling for his brother."

Mr Doug Ford announced last year that he would not run for re-election as councillor, saying that he wanted to focus on his brother's re-election.

Mr Michael Ford, the nephew who withdrew from a city council race to allow his uncle to run in his place, is now running for the city school board.

The Fords' politician father Doug Ford Sr. died of colon cancer less than three months after being diagnosed in 2006.

In 2009, doctors removed a tumor from Mr Rob Ford's appendix, and the then-city councillor returned to work in good health.

Medical experts said Mr Ford will likely require surgery regardless of whether the tumour is cancerous or benign, and said the biopsy is typically quick and uncomplicated.

In May and June, the mayor underwent rehab for drug and alcohol abuse. He emerged noticeably thinner though still obese. Mr Ford said he regretted not getting treatment "years ago" to treat his alcohol addiction.

Mr Ford, who came to power in 2010 pledging to cut waste at city hall and keep a lid on taxes, has a core base of suburban support known as Ford Nation.

A poll released on Wednesday showed Mr Rob Ford running in second place with 28 per cent of the vote, behind conservative front-runner John Tory, who had 40 per cent of voter support. Left-leaning candidate Olivia Chow was in third place with 21 per cent of the vote.