The person spoke on condition of anonymity because the deal is pending Benoit passing a physical.
In his first season as Tigers closer, Benoit had 24 saves in 26 chances. But in Game 2 of the AL championship series, he allowed a tying grand slam by Boston's David Ortiz that was a turning point in the series.
A starter early in his career, Benoit has been strictly a reliever since 2006 while with the Texas Rangers. He is 44-35 lifetime with a 4.11 ERA and 37 saves.
Benoit, who turns 37 on July 26, is expected to replace setup man Luke Gregerson, who was traded to Oakland for outfielder Seth Smith. He could also be insurance for closer Huston Street, who's been on the disabled list three times the last two seasons.
Street is entering the final year of a $14 million, two-year deal. The Padres hold a $7 million option for 2015.