The star will be called Siro, according to the Argentine and forward star of forward star Argentina.
Messi and his wife, Rokkuso's third child, can be born early this month or early March.
Messi confirmed the issue of having a son by posting a video to Instagram.
Messi, the five-time footballer of the year, was tied to last year's long-time girlfriend Roccusso. Two sons, Tiogo and Mateo, were born in their house before marriage.