Clark has forged a rivalry with judge Gary Barlow since the beginning of the live shows, with Barlow frequently voicing his dislike of the Essex-born contestant.
Barlow has described Clark's performances as "embarrassing" and has told the other panellists they should be ashamed of having put him through to the live stages.
However, Williams has publicly lent his support to Nicole Scherzinger's act, tweeting: "TEAM RYLAN ALL THE WAY. VOTE RYLAN."
Barlow responded to the support by joking that his friendship with Williams was instantly over.
"It was going so well between the two of us, 20 years knowing each other," he said.
"We did an album together and it's all over in one tweet. In five letters it's all over!"
Rylan Clark has said that he wants to eventually become friends with Gary Barlow.
Take That were recently reported to be planning a new album and tour in 2013.
X Factor acts and judges partying in London:
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