The actor and singer bumped into the X Factor contestant backstage at ITV studios last weekend, but Clark got him confused with another performer.
"A tall, scary character came leaping towards me. Hairspray, mascara. Yes, it was Rylan," he said on his Heart FM show.
"He recognised me and said, 'Oh no, it's Darren Day!'
"Darren Day! I couldn't believe it. Last week, my daughter said I look like Daniel Craig. Not quite as aspirational this week, but I'll survive. Will Rylan though?"
Clark recently said that he will "definitely go on the pull" with Katie Price in the near future.
Donovan is hoping to schedule a long-awaited duet with Kylie Minogue at the PWL Hit Factory concert in December.
The X Factor continues with a number ones-themed show on Saturday (November 3) at 8.20pm on ITV1.
Photo gallery - X Factor results show 4:
Copyright: Ken McKay/Thames/Rex Features