While many covered up in the cold, Serena Williams spent Christmas in what looked like underwear.

The 42-year-old tennis player spent the festive day enjoying some water sport activities in a very skimpy bikini.

Serena looked happy and relaxed as she ate lunch aboard a yacht with her friends in Miami, Florida.

Unusual bikini: Serena Williams’ swimwear looked more like underwear as she ate lunch on a yacht in Miami

Skimpy look: The 42-year-old wore a black lace and white halterneck bikini top with a pair of plain black bottoms

Safety first: The tennis played donned a life jacket as she prepared to enjoy some water sports activities

Wearing a white halterneck bikini top with a black lace trim and all black bikini bottoms, the U.S. star wasn’t bothered about showing off her body.

Serena pushed her hair back with a simple headband and modelled her muscular physique as she laughed with her group of friends.

She later donned a life jacket as the group sat on an inflatable towable and joked around with one another.

Having a laugh: Williams appeared to be enjoying herself as she fooled around on an inflatable towable with her friends

Easy does it: The group looked as though they were going to fall in the water as they joked around with one another

At one point it looked as though the group were in danger of falling in the water as they piled on top of Serena.

The sports star is known for having a fuller figure and is not afraid to show it off, but her older sister Venus isn’t so confident about hers.

The 42-year-old recently admitted that she had slimmed down after swapping steak for salad.

Her sister on the other hand made the most of the U.S. sunshine and certainly appeared to have a very merry Christmas.

Sporty siblings: Serena (L) is confident about her body whereas her sister Venus recently admitted to swapping steak for salad in order to slim down