“Welcome Ciro!!! Thank God, everything went perfectly. He and his mummy are doing very well. We are super happy!!!” wrote Messi on his Instagram account, accompanying the post with a photo of the baby’s hand.
Ciro is a brother to five-year-old Thiago and Mateo, who is two.
Messi had pulled out of Barcelona’s squad for Saturday’s La Liga match at Malaga to be present for the birth.
The club tweeted: “Change to the squad. Messi is out for personal reasons and Yerry Mina takes his place.”
The Argentinian couple, both 30, first met in their hometown, Rosario, in 1996 and started going out a decade later. They were married last year in Rosario.