The 35-year-old is in the final year of a three-year, $21 million contract he signed with Minnesota in 2011. Willingham was traded to the Royals in August.
If the Royals -- who are three games ahead in the Wild Card race -- make the playoffs, it would be the first postseason trip in Willingham's career.
Willingham won a Silver Slugger Award in 2012, when he hit 35 home runs and had 110 RBI. His career totals currently stand at a .253 average, 195 home runs, 632 RBI and a .359 OBP.
- Molly Geary