The 25-year-old was given permission to leave training this morning to accompany his partner to USP Dexeus, a hospital in the city, after she went into labour.
After several hours, the boy was born just after 17:00CET, with Roccuzzo surrounded by family and friends, including Messi’s parents, Jorge and Celia.
“Today, I am the happiest man in the world,” Messi wrote on his official Facebook page.
“My son was born, and I thank God for this gift! Thanks to my family for the support. A huge to everyone.”
Despite becoming a father, Messi will be available for selection for the Blaugrana against Celta Vigo on Saturday.