Concerns on Pope Francis' health were raised anew on Monday after the 78-year-old pontiff stumbled while walking the steps towards the altar at the Basilica of St. John Lateran in Rome, the second time in three days that he nearly collapsed on the floor.

Two priests flanking him quickly came to his aid, taking both his elbows to help him reach the altar to lead a mass, reports said.

In the video footage of the incident, the Pope is seen approaching the steps confidently. But on the first step he falls backwards, the Daily Mail reported.

Upon reaching the altar with the aid of the two priests, the pope places his hand over his chest. He then proceeds to celebrate mass, which was capped by the ordination of Monsignor Angelo De Donatis as an auxiliary bishop, the Catholic News Agency (CNA) said.

It was the second time in three days that Pope Francis stumbled in public, having also tripped on the steps of St. Peter's Basilica on Saturday while celebrating mass. In that first incident, the pope escaped injury after thrusting his hands out in front as he was falling down, preventing his head from hitting the floor. Two aides quickly helped him back to his feet after the fall, according to the Daily Mail.

Last Oct. 21, the Vatican was compelled to issue an official denial of an Italian newspaper report that Pope Francis was suffering from a small but curable brain tumour, according to CNA.

Fr. Federico Lombardi, S.J., the director of the Holy See press office, denounced the report by the Italian agency Quotidiano Nazionale, calling it "gravely irresponsible."

Lombardi assured that Pope Francis was continuing with his busy daily schedule without any health issue bothering him.

"Moreover, as everyone can see, the Pope is carrying out his very intense activity without interruption in a way that is absolutely normal," he said.

Lombardi admitted though that Pope Francis has some difficulties with his leg, but "his head, it seems to me, is absolutely perfect."

The Pope is reportedly missing part of one of his lungs after he contracted a lung infection when he was still a young man.

He is also known to suffer some leg pain due to sciatica, for which he undergoes regular therapy. Sciatica is described in medical circles as the "pain affecting the back, hip, and outer side of the leg, caused by compression of a spinal nerve root in the lower back, often owing to degeneration of an intervertebral disk."

Last September during his visit to the United States, Pope Francis also had a slip-up while climbing a staircase to board a flight. But he quickly got back to his feet, without any assistance, and entered the plane without any further difficulty.

Pope Francis once said that he expects his papacy to be short. He ends every weekly Angelus address with an exhortation to the world's 1.2 billion Catholics to pray for him, the same personal appeal he makes when meeting guests.