The Brit reveals he was offered the starring role following Sheen's infamous exit from the show in 2011, and he seriously considered it because he was a fan.
But producers couldn't offer him any ideas about his character or a plot, and so he had to say no.
During an appearance on Howard Stern's SiriusXM show on Wednesday, the Notting Hill star said, "They talked to me about it, but the problem was they didn't have a script or a new character. They just said, 'Trust us. We'll create one'.
"I said, 'Well, it's very difficult for me to consider this without a script'... I said, 'Well, you're obviously brilliantly talented'. Because I like that show! And they make brilliant TV shows, really. But I said, 'I'm too scared to sign up without a script'."
Ashton Kutcher wasn't, and he landed the role of millionaire Walden Schmidt.
But Grant didn't stop being a fan of the show - he kept watching.
"It was still a very good show, but what they created for Ashton Kutcher was clearly something completely different than what they would have created for me."
Hugh told Stern that he was offered a big-money deal to take on the sitcom: "It was stratospheric. I had no idea how much TV was worth here (in America)."
You may also like: Kutcher promises best-ever season of Two and a Half Men
Kutcher and co-star Jon Cryer became the highest-paid TV actors in 2013, earning $24 million (about R 318 million) and $21 million (R 279 million), respectively.
© Cover Media