The United States' former winner Zach Johnson has withdrawn from The Open after testing positive for COVID-19 ©Getty Images

American Zach Johnson has become the latest major winner to withdraw from this week's The Open Championship in the United Kingdom after he tested positive for COVID-19.

Johnson, the 2015 Open champion, is one of 17 players to have pulled out of the final major of the season at Royal St George’s in Kent.

South African Louis de Jager, who had been set to make his debut at The Open, has also withdrawn after returning a positive test for  coronavirus.

Johnson and De Jager join a growing list of absentees from the tournament, which also includes reigning Masters champion Hideki Matsuyama and two-time Masters winner Bubba Watson of the United States.

"I am disappointed to announce that I have tested positive for COVID-19 and will have to withdraw from the 2021 Open Championship," Johnson, winner of the Masters in 2007, said on Twitter.

"I look forward to returning to St. Andrews next year, a place where I have such wonderful memories. 

"Good luck to all the competitors."

Johnson's positive test came prior to the final round of the John Deere Classic on Sunday (July 11).

The 45-year-old received news of his result prior to boarding a chartered flight carrying players over to the UK for The Open, due to begin on Thursday (July 15).

Defending champion Shane Lowry has backed the stricter COVID-19 protocols that will be in operation at The Open ©Getty Images
Defending champion Shane Lowry has backed the stricter COVID-19 protocols that will be in operation at The Open ©Getty Images

The stricter COVID-19 protocols set to be in operation at the event have also led to withdrawals.

Golfers will be required to undergo COVID-19 testing, regardless of vaccination status, and have been barred from visiting restaurants, pubs or shops during the tournament.

Players have been critical of the regulations, which are tougher than they have faced since the resumption of the PGA Tour, as they coincide with 32,000 spectators being allowed to attend each competition day.

Ireland's defending Open champion Shane Lowry, however, has backed organisers for implementing tougher rules.

"The R&A (Royal & Ancient) have done a great job and they’re doing a good job this week of trying to keep us away from as many people as they can," Lowry said. 

"I know there’s going to be 32,000 people here. 

"I think that’s great for the tournament, but us as players, I’m in my own bubble at my own house and I’m not leaving. 

"I’m not allowed to do any of that [other] stuff and I think that’s good. 

"I don’t want to be here playing in front of nobody, so I think it’s great that there’s 32,000 people and I was very excited when I heard that there was going to be that many people here."