Hioki, who boasts a 24-4-2 record, is considered by most to be among the world's top featherweights.
A winner of four straight, the 27-year-old Hioki has spent almost his entire career fighting for Japanese promotions, though he has fought a handful of times in Canada. He is currently riding a four-fight win streak and holds two wins over recent No. 1 contender Mark Hominick. He also has career victories over Marlon Sandro, Ronnie Mann and Rumina Sato.
During his career, Hioki has won some of MMA's most prestigious 145-pound championships, including the Shooto and Sengoku titles in Japan. With Sengoku in dire financial trouble, he recently vacated their belt to sign with the UFC.
Roop (12-7-1) is coming off a third-round TKO victory over Josh Grispi at June's Ultimate FIghter 13 Finale.
UFC 137 will take place at the MGM Grand Garden Arena and feature Georges St-Pierre attempting to defend his welterweight championship for the seventh time while facing former Strikeforce champion Nick Diaz.
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