Video report by ITV News Reporter Martha Fairlie
The X Factor supremo fell from a new electric bike he was testing at his house in Malibu.
The 60-year-old was taken to hospital where he had an operation on Saturday night, which involved a number of procedures including having a metal rod put in his back
Watch friend Lizzie Cundy talk about the injury
Friend Lizzie Cundy said: "We're just very lucky he's been able to get the surgery and he's going to be OK."
Cowell 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 recovering in hospital and it is understood that he will continue to do so for a few days.
A source said that while it is a bad injury, doctors said he had been very lucky.
The entertainment boss has a six-year-old son, Eric, with his partner Lauren Silverman – and it is understood Eric was with his father at the time.
A spokeswoman for Cowell said: “Simon has broken his back in a number of places in a fall from his bike whilst testing a new electric bike in the courtyard of his home in Malibu with his family.”
She said he was taken to hospital, where he was operated on overnight, adding: “He’s under observation and is doing fine.”
Britain’s Got Talent judge Amanda Holden was among the people posting messages for Cowell on social media.
Alongside a picture of the pair together on Instagram, she wrote: “I’ve been thinking about my dear friend all day and luckily I’m able to say (with blessing) that he’s had his operation and he’s doing really well, Chris Lexi Hollie and me wish you a speedy recovery and send you, Lauren and Eric all our love”.
Just last month it emerged that Cowell has bought Sony Music Entertainment’s stake in TV programmes including Britain’s Got Talent and The X Factor.
The move sees the music mogul gain ownership of all the international versions of The X Factor and Got Talent programmes.
The Got Talent format airs in 76 markets, while The X Factor is broadcast in more than 130 territories.
Sony Music’s share of the venture has transferred to Syco Entertainment, a company solely owned by Cowell.
Filming on the next stage of this year’s Britain’s Got Talent has been postponed because of the coronavirus crisis, but ITV has said it hopes to continue the series later this year.