The Take That man told Metro that he might also perform with the singer if he gets to the X Factor final.
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© WENN
"If Rylan does get to the final then maybe it will be me," Williams. "I wouldn't mind. I'd love that, I love Rylan.
"I think Kylie Minogue might do a better job with Rylan because I think she's dancey and poppy but if needs be I'll turn up if they're short."
He added: "[We'd sing] 'Islands In The Stream' which is not very Rylan but I think 'Islands In The Stream' with me and Rylan would be very entertaining.
"A disco version of 'Rylan's In The Stream', you heard it here folks."
© Rex Features
Williams had previously expressed his support for 'Team Rylan' and urged his fans to vote for him.
His bandmate and X Factor judge Gary Barlow quipped in response: "We did an album together and it's all over in one tweet. In five letters it's all over!"
Williams was a guest mentor on The X Factor last month, advising Clark and the other competitors before playing his new single 'Candy' on the results show.
X Factor results show - episode four photo gallery:
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