The Nationals placed Willingham on the 15-day disabled list on Thursday. Manager Jim Riggleman says Willingham will have surgery next week to repair a medial meniscus tear in his left knee. Riggleman says it is unlikely Willingham will have time to recover from the surgery before the end of the season.
Thursday was the first day Morgan, who was recovering from a sore hip, could come off the disabled list.
Willingham is hitting .268 with 16 homers and 56 RBIs.