James DeGale has labelled George Groves "chinny" ahead of their May 21 showdown at the O2 Arena, London.
Groves found himself on the floor in a Commonwealth super-middleweight title defence against Kenny Anderson in his last fight.
And DeGale believes that it belied a weakness in his armoury.
"I spoke to Carl Froch, and he knocked George out in sparring," said DeGale.
"There's no shame in that because Froch is a world class fighter.
"But he was on the floor against Anderson, all over the place really, and he got knocked out as an amateur as well.
"There is something wrong with his chin, there has to be if he keeps going over all the time, and I will exploit that.
"People keep saying that I haven't been tested yet, but that's only because I keep on winning.
"Paul Smith was supposed to be a test for me and I won that fight easily.
"I hope that George is a test for me, but to be honest he's just going to make me look good."