HUMBLE, Texas — Vijay Singh has withdrawn from the Houston Open with a back injury.

Singh played nine holes, shooting a 43 with two double bogeys, before walking off the course. He also withdrew from the Transitions Championship two weeks ago with a back injury.

Singh tied for fourth at the Honda Classic and tied for 11th at the CA Championship before the Transitions event.

Earlier Thursday, defending Houston Open champion Paul Casey withdrew because of a left shoulder injury. The 32-year-old Englishman is hoping the latest injury is "just a one-week thing" and won't keep him out of next week's Masters.