Rossborough will take on the unbeaten Lorenz Larkin in the night's main event.
The switch was first reported by Sherdog.com and has since been made official by Strikeforce.
Rossborough is a seven-year veteran of the sport with an 18-13 record. He tried out for season seven of The Ultimate Fighter, but was eliminated by Jesse Taylor in the entry round and never made it into the house.
Rossborough competed as recently as last weekend, defeating Hank Weiss via second-round guillotine choke submission. Overall, he's won six of his last seven.
Larkin has yet to lose in his MMA career, going 11-0. He'll face a distinct reach advantage in this one, as he's 5-foot-11 and Rossborough is 6-foot-5. It will also be something of a style clash, as 11 of Rossborough's wins have come via submission, while Larkin prefers the striking game, and eight of his victories have come via KO or TKO.
Strikeforce Challengers takes place at The Pearl at The Palms in Las Vegas.