Lee Westwood says his season has been seriously disrupted by the injury to his caddie and new putting coach Billy Foster.
Foster could miss most of the summer after having surgery on his right knee, which he hurt before a charity soccer match earlier this month.
The No. 3-ranked Westwood will be without Foster for next month's U.S. Open and possibly the British Open in July and the PGA Championship in August, denting his hopes of landing a first major title.
Westwood says "he's an integral part of the team . my game and results have improved the last few years as a result of Billy being on the bag."
Westwood's replacement caddie is Mike Waite, who helped Michael Campbell win the U.S. Open in 2005.