(AFP) - Pope Francis has a fever that caused him to clear his schedule on Friday morning, the Vatican said, nearly two months after the 86-year-old pontiff was hospitalised with bronchitis.

"Due to a feverish state, Pope Francis did not receive an audience this morning," said Vatican spokesman Matteo Bruni, without giving more details.

It was unclear who the pope had been expected to meet with, as his agenda was not made public on Friday, as is customary.

Vatican Secretary of State Pietro Parolin blamed the pontiff's busy schedule, saying he was tired.

"The pope was tired, yesterday he had a very busy day, he saw a lot of people .. he wanted to say hello to them all," said Parolin, according to Italian news agencies.

"And probably at a certain point the resistence breaks down."

Francis had eight meetings Thursday, according to his published schedule.

The pope's morning audiences are usually reserved for heads of states, associations and clerics, while his afternoons are devoted to work and private meetings.

Next on Francis' schedule is Sunday's mass at St Peter's Basilica to celebrate Pentecost, followed by the traditional Regina Coeli prayer.

On Monday, he is scheduled to meet with Italian President Sergio Mattarella.

Francis, who has been the leader of the world's 1.3 billion Catholics for a decade, has suffered increasing health issues over the past year, from persistent pain in his right knee to sciatica to his recent hospital stay for bronchitis.

The episodes have sparked widespread concern and fuelled speculation that he might choose to retire rather than stay in the job for life, a choice made by his predecessor, Benedict XVI.

In late March, Francis was admitted to hospital in Rome after having breathing difficulties, and stayed for three nights.

He was treated with antibiotics for bronchitis.

As he left the Gemelli Hospital on April 1, the pope smiled and joked with well-wishers, quipping: "I am still alive!"

He went on to participate in Holy Week and Easter services, the most important week in the Christian calendar.

- Good days, bad days -

For about a year, the pope has had to rely on a wheelchair due to recurring pain in his knee that he has said cannot be treated through surgery.

Asked about his health in an interview with US Spanish-language network Telemundo broadcast on Thursday, Francis said it was "much better".

"I can walk now. My knee has been mending. I could hardly walk beforehand, now I can. Some days are more painful than others, like today," the pope said.

Francis added that doctors had caught his bronchitis infection just in time.

"If we'd waited a few more hours, it would've been much more serious. But I was out (of the hospital) in four days," he said.

Despite his health issues, Francis continues to travel widely, and concluded a three-day visit to Hungary earlier this month.

His next planned trip is to Lisbon from August 2-6 to attend World Youth Day, the Vatican announced on Monday.

The pope acknowledged last July, however, that he needed to slow down.

"At my age and with this limitation, I have to save myself a little bit to be able to serve the Church," he said then.

"Or, alternatively, to think about the possibility of stepping aside."

In March, however, he insisted that he had no current plans to quit.

Benedict XVI, who died on December 31 aged 95, surprised the world in 2013 when he announced he was stepping down, a radical move not seen since the Middle Ages.

© Agence France-Presse