Louis de Jager, one of 12 players to earn a spot at the Royal & Ancient Golf Club of St. Andrews through local final qualifying, is also on that list. The R&A said player Ryan Moore, the runner-up at the John Deere Classic in Illinois, turned down the exemption for the highest finisher among the top five at the PGA Tour event.

In all, 16 players have withdrawn or declined to take their spots in the field for the 149th edition of golf’s oldest championship game.

The British Open was the only major event canceled last year due to the pandemic. Though it returned this year, it is under strict regulations from the U.K. government, and some instituted by the R&A, like banning players from staying with anyone outside their small group of people.

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Johnson, who won at St. Andrews in a playoff in 2015, was at the John Deere Classic and had to be tested before getting on a charter flight. He did not play the third or fourth round with any other player who is at the British Open.

The latest players to withdraw were replaced by Adam Long of the United States, Sam Horsfield of England and Dylan Frittelli of South Africa.

The field already is missing seven players from the top 75 in the world, unusual for a major.

Some had no choice. Masters champion Hideki Matsuyama at No. 18 was the highest-ranked player to withdraw. He had a positive COVID-19 test during the Rocket Mortgage Classic on July 2, and while he has gone through 10 days of self-isolation without symptoms, his tests keep coming back positive.

The PGA Tour had this issue a year ago with positive tests. U.S. health officials said PCR tests can pick up remnants of the virus even though it is no longer active. But under U.K. guidelines, Matsuyama would need to produce a negative test.

Two-time Masters champion Bubba Watson said he came in contact with a person who had a positive COVID-19 test and withdrew. Under the R&A requirements sent to players on June 22, anyone who is identified as a contact has to self-isolate and be withdrawn.

Other players cited international travel requirements (Kevin Na) or an emphasis on preparing instead for the Olympics (Sungjae Im, Siwoo Kim, Juvic Pagunsan). The men’s competition in the Tokyo Olympics starts 11 days after the British Open ends.