The millionaire founder of the Maximuscle nutrition brand was airlifted to hospital after a crash at a high-speed racing event.
Zef Eisenberg was riding a gas turbine engine motorbike at the Straightliners Top Speed meeting at Elvington Airfield in North Yorkshire.
The 43-year-old fell from his Madmax Turbine bike during a during timed track run at 14:00 BST.
It is understood he has a suspected broken pelvis.
The event is a gathering of vehicles to attempt land speed records.
A spokeswoman for the Madmax race team, owned by Mr Eisenberg, said he "had an accident racing" and was taken to Leeds General Infirmary. He is understood to have sustained a suspected broken pelvis.
She added: "He is in a stable condition and is receiving the very best care."
Guernsey-based Madmax is a specialist engineering team focusing on extreme motor bikes, quad bike and land speed racing