Simon Cowell is 'walking again' as Kelly Clarkson fills in for him on 'America's Got Talent'

Simon Cowell is "walking again" days after undergoing a five-hour surgery for the back injuries he sustained when he fell off an electric bike at his Malibu home on Saturday.

However, he had to miss filming of the first week of "America's Got Talent" as he recovers from the injury, and was "grateful" when Kelly Clarkson stepped in to fill for him on Tuesday and Wednesday's live episodes of the show.

"He's on his feet and walking around again as much as he can," a source told People magazine, adding that the 60-year-old is in "good spirits" as he recovers from his multiple back injuries.

The insider revealed that the executive producer continues to stay under the observation of doctors at the hospital where he got a number of fusions and a metal rod put into his back on Saturday night.

"He's taking it easy but doing well," the source said, adding that the father-of-one has already started sorting through whatever work can be done from his hospital bed. "Simon is already back at work and he's been working on email on his iPad and speaking to a few on his team. He's definitely not letting this slow down all the things he's got going on," the source said.

However, Cowell had to take a couple of days off from AGT which started filming just a day after his accident. The show asked Clarkson to stand in for Cowell for two episodes, as confirmed by the "Stronger" singer through her Twitter account.

"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 38-year-old quipped in her tweet.

The source told People magazine that Simon is "really happy" that "The Voice" judge is standing in for him on AGT this week and he is "grateful to her." While the source added that Cowell is back on his feet, a report in The Sun suggests otherwise and claims that the telly mogul won't be able to walk for weeks.

A source told the outlet that doctors have warned Cowell he faces a long and difficult recovery that will involve intensive physiotherapy and wearing a back brace, which is "going to take him weeks, maybe months."