Serena Williams has revealed she is about to retire from tennis, announcing "the countdown has begun" with the US Open seemingly set to be her final tournament.

With 23 grand slam singles titles, Williams is the most decorated player of the Open Era, but her most recent major success came at the 2017 Australian Open.

The 40-year-old is one title shy of Margaret Court's all-time record and appears set for one last shot at matching the Australian.

In a long piece in Vogue, Williams wrote of her plan to "move in a different direction" after "these next few weeks".

Williams has already been named on the entry list for the US Open, which starts at Flushing Meadows at the end of August.