Kaley Cuoco almost had her leg amputated after a horse riding accident.

The 36-year-old actress - who is expecting her first child with boyfriend Tom Pelphrey - was riding at a Los Angeles ranch in 2010 when her horse got spooked and she fell off, before the equine tried to jump over her and landed on her left leg, resulting in her being rushed to hospital with severe injuries.

'Big Bang Theory' creator Chuck Lorre recalled in Jessica Radliff's new oral history book 'The Big Bang Theory: The Definitive, Inside Story of the Epic Hit Series': "That was the darkest, most frightening time in all twelve years [of the show].

"Kaley could have lost her leg. It was a series of miracles that allowed us to get through that and for her to come out the other end of that healthy."

Co-star Johnny Galecki added: "They were talking about amputating her leg, which was devastating to hear."

Doctors originally believed the actress wouldn't walk for months but after two weeks in hospital, she was fitted for a walking boot and was back on her feet.

And Chuck thinks it was "heaven-sent" that he ran into Dr. Stephen Lombardo, of the Kerlan Jobe Orthopedic Clinic for Sports Medicine at Cedars-Sinai, and asked for help with the actress' injury.

He added: "It was an absolutely miraculous intervention that I ran into Dr. Steve. Every time I see him, I say, 'Thank you! You saved Kaley! On a lesser level, you saved 'The Big Bang Theory'!'"

In less than two hours after their meeting, Kaley was "in surgery with the best surgeons available to stop an infection because her leg was wide open."

In an excerpt from the book obtained by People magazine, Kaley admitted the accident is still "too much" for her to talk freely about.

She said: "Before I went into surgery, they made me sign something that said, 'We don't know until we get in there and see this leg, and it could come out that you don't have it anymore.' That wasn't the case, obviously, but I had to sign something that said, 'OK, you can.'

"Everything ended up fine, and I was up and working a week later, but the doctors acted like I was never going to walk again. It's still too much for me to go into, and it sounded way worse than it was. And of course it was spiraling and everyone was freaking out, which I get. It scared people."

Johnny added: "But I think it scared people in a good way, myself included. The first day I saw you in that state, I just shed tears in my garage."