Willingham was optioned to Triple-A Rochester on Sunday, Mark Zuckerman of MASNSports.com reports.
Willingham joined the Nationals on Sept. 1 for his latest stint in the majors, and he had a 3.48 ERA, 1.55 WHIP and 4:5 K:BB over 10.1 innings during his time with the big club. His overall numbers in the majors this year are much worse with 18 earned runs allowed in 24.1 frames.