The American has won the race for the last four years and had been hoping to become the first athlete in the event’s history to win five consecutive titles.

But the 16-time Paralympic Games medallist has decided to withdraw after finishing fourth in the Boston Marathon on Monday (April 18).

It was the first time she had not won the race 2012 but still saw her crowned the inaugural Abbott World Marathon Majors women’s wheelchair champion.

McFadden, however, has been forced to visit hospital twice i the last two months with life-threatening blood clots in her legs and decided she could not afford to risk competing again so soon after Boston. 

"In February, I was diagnosed with blood clots in my legs and admitted to hospital for an operation," McFadden, who turned 28 today, said.

"I still wanted to do both races, but after the Boston Marathon on Monday I realised that for health reasons I would be better off not taking a long flight to London.

“I am bitterly disappointed not to be coming back to defend my London title and try for a fifth victory but I have to listen to my body and Monday’s race told me it is just not ready to take on two such challenging events and a long-haul flight."

In her absence, Switzerland’s Manuela Schär will be favourite to win the London Marathon for the first time.

Schär has been second to McFadden for the last three years and in Boston earlier this week smashed the course record by nearly six minutes in 1 hour 28min 17sec when she recorded the fastest women’s wheelchair marathon in history.