Serena Williams spent Christmas day frolicking with friends on Miami Beach, but wore an ill-fitting bikini that was a size too small.

The tennis champ was accompanied by friends on the relaxing day as they indulged in water sports and lounged on the beach. Flaunting her incredibly ripped body, Serena wore a black and white two-piece bikini that looked as though it were a size too small.

While her cleavage struggled to stay in the confines of her top, the bottoms appeared to be lost in Serena's famous derriere.

Meanwhile, it was announced earlier this week that Serena and her sister Venus will be taking part in the Australian Open which begins in January.

Check out the pics of Serena on the beach in the gallery below.

Serena Williams wears ill-fitting bikini on Miami Beach on Christmas Day...