Pope Leo XIV's health should not be taken "for granted", a British senior Vatican official told the BBC.
Archbishop Paul Gallagher, the Vatican's foreign minister since 2014, said the news of the Pope's ill health was "a bit of a game changer", adding "it's going to make things a bit different".
The Pope was diagnosed with lung adenocarcinoma following surgery to remove a lower lobe of his right lung.
Speaking on Tuesday after the Pope's operation was announced, but before his cancer diagnosis, Archbishop Gallagher said: "I think we were maybe taking him a little bit for granted."
The 71-year-old had surgery at Rome's Gemelli Hospital on Tuesday afternoon, which the Vatican said had been "successful" and proceeded without complications.
Speaking to Radio 4's the Sunday Programme, due to air this weekend, the Archbishop said: "It's in some ways I think going to be a bit of a game changer after having the latter years of Pope Francis when he was in the wheelchair.
"And Pope Leo comes along and he's sporty and he seems to be in excellent health, and now we're told that he's not in excellent health and things have got to be sorted out."
Asked how it will make things different going forward, the Archbishop said church figures might have assumed "that he was not quite like the rest of us who are very aware of our vulnerabilities and the ageing process".
He went on: "But lots of us have been through similar experiences at different times in our lives, and we've got through them, and so we hope it's going to be the same case with Pope Leo.
"I am concerned. I think we've got to ask the question: how was it discovered? What happened?"
The Vatican has said the Pope is showing steady improvement in hospital, and he was expected to lead Sunday prayers.
They had stressed that the Pope had shown no symptoms of infection or illness prior to the procedure.
The Angelus prayer is traditionally recited at the Vatican, overlooking crowds in St Peter's Square but has sometimes been given from a hospital window by previous popes when necessary.
No date has been given for Pope Leo's hospital discharge, but recovery was expected to take around a week.
Leo himself announced the news of his operation during his weekly Sunday prayers, telling the crowd in St Peter's Square that doctors had found a nodule on his lung.
Nodules are quite common and not necessarily cancerous, but after it was examined the medical team confirmed it was, "as suspected by pre-operative tests", the Vatican said.
Archbishop Gallagher, who is from Liverpool, also said he expected the Pope to visit the UK at some point.
"We have exchanged a little bit," he said. "He's just beginning to think about what he might do in 2027, but it's still very much at the examining the possibilities (stage)".
He would "bring a spirit of renewed hope", said the Archbishop, after the Pope received a rapturous welcome in France and Spain earlier this year.
"But these things do take quite a lot of planning, and so you don't just do it overnight."
You can hear more of Archbishop Gallagher's interview on The Sunday Programme on Radio 4 at 0710