The head of Atlético Madrid's medical team has been summoned to the Vatican to help treat Pope Francis, who is suffering from an arthritic knee.
The 85-year-old Pope has cancelled various activities in recent months, including a trip to Africa, because of mobility problems.
José María Villalón said the Pope was "very nice" but also "very stubborn" as he refused to undergo surgery.
The Pope is a big fan of Argentinian club San Lorenzo - not the Madrid club.
San Lorenzo's football base is Buenos Aires, where the pontiff - Jorge Mario Bergoglio - was born.
Since May the Pope - leader of more than a billion Roman Catholics worldwide - has walked with the aid of a stick, or used a wheelchair.
In an interview with Spanish radio station Cope, Dr Villalón said "I am optimistic the Pope can be helped", but he admitted that the Pope's busy schedule made treatment more difficult.
He also admitted that, at his first meeting with the pontiff, he was "very nervous" because of the responsibility of this new challenge.
"More conservative treatment will have to be offered," he said, because the Pope is refusing surgery, having had a colon operation in July last year. The Pope's arthritis causes swelling of his joints, he explained.
"He has a great personality, he's doing well, very lucid, he's a very grateful man, very friendly and pleasant. He also likes football," Dr Villalón said.
The medic has been helping Atlético Madrid's footballers since 1995. He is a specialist in orthopaedic surgery and traumatology.