Serena Williams has shared a sweet snap of her baby daughter flexing her "biceps" in her sleep.

The tennis champion and her Reddit co-founder fiance Alexis Ohanian welcomed daughter Alexis Olympia Ohanian, Jr. on 1 September (17), with the proud parents taking to Instagram to post some cute photos of their baby on her own account on Friday (15Sep17).

In just the second photo uploaded to the picture-sharing platform, baby Alexis is seen in a pose that looks very similar to someone proudly showing off their biceps.

Alexis is dressed in a baby grow printed with the words, "Smart and Strong like my Mama", while the snap has been simply captioned "Biceps".

The little girl was first introduced to social media on Wednesday, when Serena, 35, posted a photo of Alexis resting on her chest.

"Meet Alexis Olympia Ohanian Jr.," she captioned the adorable picture. She also posted a video montage which she and her fiance had made in the lead-up to the baby's birth, in order to document the child's "amazing journey".

The fascinating video begins with a shot of Serena's ultrasound photo and goes on to show the star blossom week by week. Also included in the family video are clips of Serena and her 34-year-old beau putting together the baby's nursery, and footage of the athlete playing tennis.

The Wimbledon champion previously revealed she found out she was expecting her first child with Alexis while she was preparing for the Australian Open in January.

The couple didn't find out the sex of their baby until she was born but Serena had been convinced she was having a girl.