Tired Pope Francis says he needs to pull back on travel or possibly retire

Pope Francis acknowledged Saturday that he can no longer travel like he used to because of his strained knee ligaments, saying his weeklong Canadian pilgrimage was "a bit of a test" that showed he needs to slow down and one day possibly retire.

Speaking to reporters while traveling home from northern Nunavut, the 85-year-old Francis stressed that he hadn't thought about resigning but said "the door is open" and there was nothing wrong with a pope stepping down.

"It's not strange. It's not a catastrophe. You can change the pope," he said while sitting in an airplane wheelchair during a 45-minute news conference.