The music mogul underwent six hours of surgery on Saturday after falling from an electric bicycle he was testing at his house in Malibu, California.He is understood to have been with his six-year-old son Eric at the time of the fall, and his partner Lauren Silverman accompanied him to hospital.
Cowell is now recovering from his surgery, which involved a number of procedures including having a metal rod put in his back.
One unnamed source described his fall as very bad, and doctors are reported to have said he is very lucky.
While Cowell recuperates, singer Kelly Clarkson has agreed to act as a judge on America’s Got Talent in his place.
Ahead of the live programme, which airs in the US on NBC, the former American Idol winner teased her appearance on Twitter, telling fans: “I really need to work on my British accent…”
She later posted a short video in which she sat in Cowell’s judging chair during rehearsals, with the comment: “I think I could get used to this!”.
She joked: “Um, Simon, don’t hurry back… I’m getting real comfortable in your chair. I look pretty good in it! I’m just kidding, get well!”
Luckily, the notoriously prickly Cowell didn’t take offence, tweeting after the programme: “Thank you Kelly Clarkson. Miss all of you. What a Great Show.”
The 38-year-old had shared the news she would be filling in earlier this week with an equally jokey spoof “urgent memo” on Instagram.
Posted on NBC headed notepaper, she wrote: “My friend, Simon Cowell, is doing better now but was in an accident and won’t be able to make Tuesday and Wednesday’s live shows for AGT, but no worries America, someone far wiser, cooler and hotter is taking his seat!”
“The unbelievably amazing Kelly Clarkson. You’re welcome in advance.
Following his operation, Cowell joked about his bike skills and thanked medical staff for their care.
He tweeted: “Some good advice… If you buy an electric trail bike, read the manual before you ride it for the first time. I have broken part of my back. Thank you to everyone for your kind messages.”
A second message read: “And a massive thank you to all the nurses and doctors. Some of the nicest people I have ever met. Stay safe everyone Simon.”
Cowell is the creator of America’s Got Talent and serves as a judge on the show.
He has also been the judge on Britain’s Got Talent, The X Factor and American Idol.
Clarkson won American Idol in 2002 and has since sold more than 25 million albums and 45 million singles worldwide.