The Pope, 85, told reporters on his plane back to Rome that retirement was “not a catastrophe … you can change the pope.”
The pontiff, who has suffered knee problems and has recently been using a cane or wheelchair to move, said his week-long pilgrimage in North America had been “a bit of a test” that showed the limits of his advanced age.
“I don't think I can go at the same pace as I used to travel,” he said. “I think that at my age and with this limitation I have to preserve myself a bit in order to be able to serve the Church, or decide to step aside.”
Francis's predecessor, Benedict XVI, became the first pope to step down in almost 600 years when he announced his retirement on health grounds in 2013.
“The door is open,” Pope Francis said. “It is one of the normal options. Until today, I did not use that door. I did not think it was necessary to think of this possibility but that does not mean that the day after tomorrow I don't start thinking about it.”
Pope Francis in Canada — in pictures
His continuing knee therapy forced him to cancel a trip to the Democratic Republic of Congo and South Sudan that was scheduled for the first week of July, and his health problems have fuelled persistent speculation about his future.
He said he hoped to reschedule his Africa trip, go ahead with a visit to Kazakhstan in September — where he could meet Kremlin ally Patriarch Kirill of Moscow — and would like at some stage to go to Ukraine.
But the Pope's Canadian trip was difficult and featured several moments where he appeared in pain as he got up and sat down, and he sat in a wheelchair while speaking to reporters on the plane.
“I have all the goodwill but we will have to see what the leg says,” he said.
Canada was Francis's 37th international trip since he was elected in 2013 and the pace was slower than on some earlier tours, with two events a day and long periods of rest time.
He used the trip to offer a historic apology for decades of abuse of Indigenous children at residential schools run by the Catholic Church.
About 150,000 children were removed from their families over many decades to attend the schools, in what Prime Minister Justin Trudeau called one of the darkest chapters in Canada's history.