Underwood, 32, gave birth to her and husband Mike Fisher's first child, Isaiah Michael Fisher, a month ago but refrained from posing a snap of the tiny tot on the social media.
The country singer uploaded a picture of the little one asleep with a mini hockey stick lying across him as a token to Fisher's ice-hockey team.
She captioned the adorable image, "The Predators are in the playoffs! Just waiting to get called up! #PutMeInCoach (sic).