The 16-year-old Wie from Honolulu failed to break par all four rounds at Royal Lytham & St. Annes in England and finished 13 strokes behind winner Sherri Steinhauer. Wie dropped to seventh from second in the latest women's world rankings.

She received a two-stroke penalty after the second round when rules officials determined that she made contact with a piece of moss behind her ball while taking her backswing in a greenside bunker.

Wie's agent, Ross Berlin, said in a statement that Johnston's "departure comes as part of Michelle's maturation as a golfer, part of which is learning from many different bright golf minds." No other reason was given for Johnston's dismissal, and Wie hasn't hired a replacement.

Wie entered the Women's British Open coming off a runner-up finish at the Evian Masters in France. In this year's other three women's majors, she finished third at the Kraft Nabisco Championship and the U.S. Women's Open, and fifth in the LPGA Championship.

Johnston had caddied for Wie since she turned professional in October. He previously spent 12 years with Juli Inkster, winning four major titles.

Johnston told Golf Digest that he was informed of the firing in a cell phone call from Berlin while waiting for his return flight at the airport in Manchester, England, on Monday.

"I was shocked and surprised, I thought we had a successful year," Johnston told Golf Digest. "And I was extremely disappointed that no one named Wie gave me the news."

Wie isn't scheduled to play again on the LPGA Tour until October at the Samsung World Championship. She is also scheduled to play in September at the men's European Masters and the U.S. PGA Tour's 84 Lumber Classic.