The pop icon is said to have turned down Brian May and Roger Taylor’s approach after impressing the pair when they teamed up on a 2001 re-recording of ‘We Are The Champions’ for the movie A Knight’s Tale.
But Robbie says his “low self-esteem” ultimately prevented him from following on from Freddie Mercury.
He told SiriusXM: “Even though I’m very confident here on the microphone, I have very low self-esteem.
“And I just thought I’d save them the audacity of me even trying to step on a stage and be the same echelon as Freddie Mercury. He, to me, is angelic. He’s godlike. It was just too scary.”
He added: “I was doing stadiums myself at the time. I didn’t want to have to split it three ways, but that’s another story.”
Despite being spurned by Robbie, Queen went on to recruit Bad Company singer Paul Rodgers in 2004, with their collaboration coming to an end in 2009 after global tours.
Since 2011, they have been fronted by former American Idol star Adam Lambert, with Williams praising his “incredible” voice.
“Adam Lambert – if he wasn’t such a lovely person, which he is – I would just be terrified of him because of his pure talent. His voice is absolutely incredible,” he said.
“And he’s an incredible performer, and a lovely person to boot. I’m really pleased when I meet people that I’m just overawed by their talent – he gives me a talent hard-on – and they’re nice.”
“It’s much better than meeting people that give you a talent hard-on and they’re arseholes. You’re just like, ‘Oh, I hate everything you’ve done now,’” Robbie said.
Meanwhile, Queen and Adam Lambert recently played the band’s setlist from their iconic 1985 Live Aid concert for Fire Fight Australia, the massive Australian bushfire benefit concert.
Brian May had previously described Fire Fight Australia as a benefit concert “a bit like Live Aid” when he initially revealed that Queen had been approached to play the event.