B.J. Penn (Pictures) and Diego Sanchez (Pictures) have agreed to fight on the undercard of the heavyweight title fight between UFC champion Randy Couture (Pictures) and challenger Gabriel Gonzaga (Pictures), Aug. 25 at the Mandalay Bay in Las Vegas, a source speaking on the condition of anonymity told Sherdog.com.

The 28-year-old Penn (11-4-1) recently finished longtime rival Jens Pulver (Pictures) in a lightweight clash on the finale of The Ultimate Fighter 5. Meanwhile the 25-year-old Sanchez (17-1-0) has not fought since suffering the first defeat of his career, a decision loss to Josh Koscheck (Pictures) in April.