Ryan Carr-Ketu has kicked the hornet's nest ahead of his boxing bout with Paul Gallen, invoking the Cronulla peptide scandal.

The Sharks NRL skipper used Thursday's weigh in to offer the 34-year-old double or nothing on the prize purse if he makes good on his promise to knock him out.

Carr-Ketu returned fire with a jab about the Sharks' supplements saga and Gallen's ASADA ban, setting off a war of words ahead of their heavyweight bout at Southern Cross Group Stadium on Friday.

"I've been put on the spot here a little bit," Carr-Ketu said in knocking back Gallen's wager.