"I'm devastated. It's heartbreaking," Cowell told The Sun.
Johnson stunned viewers with her bizarre performance of Duffy's 'Mercy' in the first show of the new series. Producers may now be forced to scrap footage of the singer's appearance at Boot Camp.
Cowell continued: "I really feel for her. I'm very upset and disappointed. The advice I'm given is she can't do the show. But there's another argument that we're depriving her of the chance to make some money. Even if she didn't win, she could have picked up money for personal appearances."
He added: "On the other hand, if we don't take the advice we're irresponsible."
The newspaper revealed that Johnson had performed Lady GaGa's 'Bad Romance' in a leopard print bra and hotpants at Boot Camp - filmed last month in front of Cowell, Louis Walsh and Nicole Scherzinger.
"Nicole and Louis kept giggling and Simon was in disbelief," a source said.
Johnson told the paper that she did not hide her medical problems intentionally.
"I just wasn't sure how much I was supposed to say," she said. "I'm very upset. I think people want to hear more of me and they will be disappointed by this."
She added: "It's not fair. I want another chance."
