The Shamrock-Coleman matchup had been discussed but no agreement was reached.
The July 17 card is one of three Impact FC events happening the same month in Australia and New Zealand. Murilo "Ninja" Rua has been booked to fight Jeremy May on July 3, and Paul "Semtex" Daley is in discussions to compete on the same card. Josh Barnett will meet Geronimo "Mondragon" Dos Santos on the July 10 card.
Shamrock, 46, will be competing for the first time after a one-year suspension due to a positive test for steroids for a fight in February 2009, where he won on a self-produced local card by first-round submission. It was Shamrock (27-13-2)'s first win in nearly four years.
Rizzo, 36, is a former UFC heavyweight title contender and last September defeated Jeff Monson to snap a two-fight losing streak. Rizzo (17-9) holds wins over Andrei Arlovski, Josh Barnett and Mark Coleman. Before he meets Shamrock, Rizzo has a fight this weekend against another UFC and PRIDE veteran, Gary Goodridge.