Wallace made the comments during a radio appearance on "The Mike Gallagher Show", in which the two began joking about Gallagher's weight, reported Aceshowbiz.
Then with one comment, Gallagher, 54, reportedly brought up Clarkson, 32.
"Listen, don't fat shame me. You do a lot of fat shaming," Gallagher said, according to an audio and transcript by Media Matters.
"That's the new phrase now, 'fat shaming.' Have you seen Kelly Clarkson? You know the singer, Kelly Clarkson? Holy cow, did she blow up." At first Wallace, 67, did not engage.
Van Susteren, 60, criticised the exchange on her blog. "This 'guy snickering' about her weight is obnoxious. He should apologise," she wrote.
Neither Clarkson nor Wallace have publicly commented, but Clarkson has long battled excessive scrutiny over her weight.
