The Emmerdale star was treated for injuries to his legs and knees, as well as shock, following the incident, which took place in front of his wife Joanna Page.
Thornton, who plays farmer John Barton on the soap, said that he was lucky to be alive.
An Emmerdale source told the Daily Star the entire cast was shocked. "He was having a few days off in London with Jo and they’d been out for dinner when he was hit by the car. Joanna was in a right state and James was in absolute agony.
"He knows he was lucky. We have no idea when he’s going to be back."
The incident has led to show bosses being forced to rewrite a number of scenes incolving Thornton's character.