22 July 2010 Last updated at 10:17 ET

James Cracknell in hospital with skull fracture

Fogle (l) and Cracknell had been due to ride from Canada to Mexico

Olympian and TV adventurer James Cracknell is in hospital with a skull fracture after being knocked off his bike in the US.

A spokeswoman for the star said: "He is conscious and his condition is stable. Doctors have said he is making very good progress."

The 38-year-old, who is in Arizona filming for the Discovery Channel, was hit from behind by a truck.

His wife, TV presenter Beverley Turner, is with him in hospital.

Close friend and fellow adventurer Ben Fogle (Benfogle) posted a message on micro-blogging site Twitter.

"James has been in a cycling accident in the US. My thoughts are with James and his family. Flying out to Phoenix hospital tomorrow," he said.

"Thanks for all your messages. I will keep you all posted on his condition."

Cracknell was filming for Discovery series Cracknell's Race Across America, in which he was to attempt running, cycling and rowing across the US in 18 days.

The host was not being filmed when the accident happened.

Cracknell and Fogle had been due to attempt a record-breaking bike ride from Canada to Mexico for a BBC Two series, but that has now been put on hold.

A BBC spokeswoman said: "We wish him a full and speedy recovery and our thoughts and best wishes are with him and his family."

In 2005, they took part in an Atlantic rowing race, while Cracknell has undertaken a number of cycling challenges.

Last year, Fogle became ill with a potentially fatal flesh-eating bug following a trip to Peru while filming the BBC series Extreme Dreams.