Serena Wiliams is believed to be worth £52million

Serena Williams has spoken out about her emergency operation to remove a blood clot 'the size of a grapefruit' from her stomach.

The tennis ace first felt unwell on 18 February but didn't realise something was seriously wrong.

'I am lucky to be alive, I could have died,' Serena, 29, told The Today Show.

'I had a lot of swelling in my leg - the tell-tale sign of an embolism - and I could not breathe.'

Serena's physio 'forced her' to go to the emergency room where a pulmonary embolism - which had travelled from her leg to her lung - was diagnosed.

'When I first went, at first the doctors couldn't find anything,' she recalls. 'So they said I should get a CAT scan and they found several blood clots. 

'They wanted to check me in immediately or it wasn't going to be a good result.'

A week later, after treatment, Serena travelled to LA for the Vanity Fair Oscars party, to cheer herself up, and ended up back in hospital.

'I'm on bloody thinner injections, which I give myself,' Serena explains.

'I developed a large haematoma in my stomach. I apparently must have hit something. What started out the size of a golf ball ended up the size of a grapefruit.' 

Serena is now recovering at home after the haematoma (a solid swelling of blood) was surgically removed.

'Thankfully everything was caught in time,' says Serena's rep.