The Robster hit out at former Pussycat Dolls star Nic in an interview with The Sun's TV magazine.
He said: "Nicole keeps calling him 'Gary Borelow' – well she's Nicole S***singer.
"Gary is the most talented out of the lot of [the judges], the captain. He's doing a great job as head judge. He's funnier this season than the last, which is great because he's way more funny than me.
"I've still got my Gary Barlow crush. I love him to bits."
And Robbie, 38, also told the magazine about life with his new daughter Theodora.
"Our lives are better because of her. The house is full of love," he said.
"Everyone is telling me: 'She's beautiful' but a lot of parents have a blind side when it comes to their own child so I'm holding off judgment. There are some pretty ugly babies!
"But I love her, I know that. I rap to her, grown-up songs — nursery rhymes are a bit crap and really boring."