Sixth-ranked Ian Poulter withdrew from the Zurich Classic of New Orleans on Wednesday, citing a left knee injury.
Steve Stricker, No. 3 in the Official World Golf Ranking, also pulled out of the event with a right shoulder injury.
Mark Hensby and Billy Mayfair replaced them in the field.
Poulter tied for 10th at the Masters two weeks ago after sharing the 36-hole lead with countryman Lee Westwood. The Englishman won the World Golf Championships-Accenture Match Play Championship in February for his first career PGA TOUR title and was slated to play in the Zurich Classic for the fourth time.
Stricker, who won at the Northern Trust Open in February, snaps an 11-year streak of playing in New Orleans. His best finish was a tie for fourth in 2000.