Mousasi (31-3-2) is unbeaten since losing the 205-pound belt to “King” Mo Lawal in April 2010, including a draw against Keith Jardine in Strikeforce in April and first-round TKO of Hiroshi Izumi to defend his DREAM title in July.
St. Preux (11-4), who played football at the University of Tennessee, topped Abongo Humphry in January for his third unanimous decision win in less than two months, then returned to the cage in July with a 72-second stoppage of Joe Cason.
The Dec. 17 event is also expected to feature lightweight champ Gilbert Melendez vs. Jorge Masvidal, the return of Gina Carano, and UFC vet Keith Jardine.
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Pictured: Gegard Mousasi