Jorge Mario Bergoglio, elected as the new pope on Wednesday, is a fan of San Lorenzo who lives in "a permanent state of suffering" for the Argentine club.
The pontiff, the first Pope Francis, was given membership of the club after saying mass at a sports complex near their Estadio Pedro Bidegain home in Buenos Aires four years ago.
After Bergoglio was confirmed as the new leader of the world's Catholics, San Lorenzo - who last won the Argentine title in 2007 - posted a picture of him holding a club pennant on the homepage of their website.
Oscar Lucchini, the man who handed Bergoglio his club membership card, said: "He says he lives in a permanent state of suffering for San Lorenzo."
The new pope became a fan of the club during his time as Archbishop of Buenos Aires. He was known for leading an unextravagant lifestyle during his time in the post, using public transport to travel around the city.