By Karen Crouse

Rory McIlroy posted a photograph on Instagram after injuring his ankle playing soccer. 

The highly anticipated showdown between Rory McIlroy and Jordan Spieth at next week’s British Open is in doubt after McIlroy injured his left ankle over the weekend while playing soccer.

McIlroy, the world’s No. 1 golfer and the defending Open champion, said he sustained a “total rupture” of his left anterior talofibular ligament in a “soccer kickabout” with friends in Northern Ireland on Saturday. In layman’s terms, he sustained a Grade 3 ankle sprain while playing five-on-five with friends on a less-than-pristine field.

McIlroy posted a photograph on his Instagram account on Monday of him standing on crutches with his left foot in a walking boot.

McIlroy has not ruled out playing in the British Open. He plans to make a decision later this week after seeing how the swelling in his ankle responds to rest, anti-inflammatories and ice, which are the standard treatments for his injury.

The Old Course at St. Andrews, the site of the Open, was expected to provide a worthy stage for perhaps the most compelling chapter in the burgeoning rivalry between McIlroy, 26, and Spieth, 21, who is halfway to a calendar Grand Slam.

The last time the tournament was held in St. Andrews, in 2010, McIlroy finished tied for third. Spieth was a rising senior in high school and did not compete.

With 10 top-10 finishes, including three victories, in 16 PGA Tour starts this season, Spieth has made up huge swaths of ground on McIlroy in the world rankings. If McIlroy is sidelined the rest of the summer, he could lose his crown to the second-ranked Spieth, who can ascend to No. 1 by his 22nd birthday at the end of the month with a top-five finish at this week’s John Deere Classic and a win in the British Open.

Spieth, who played in a charity event of the former Masters champion Zach Johnson on Monday in Cedar Rapids, Iowa, wished McIlroy a “speedy recovery” in a statement released by his agent, Jay Danzi. “It’s unfortunate, and you never want to see a fellow competitor injured,” Spieth said. “I hope he will be back very soon."

McIlroy was scheduled to play in four of the next six weeks, beginning with the Scottish Open on Thursday. Included in that stretch is the final World Golf Championships event of the season and the fourth major, the P.G.A. Championship, which McIlroy won last year.

The Scottish Open organizers released a statement Monday saying that McIlroy had withdrawn from the tournament.

“Rehab already started,” McIlroy wrote on Instagram, adding, “Working hard to get back as soon as I can.”

McIlroy is one of the fittest players on the tour, but his injury is a tricky one for golfers. The left ankle plays an important role in the golf swing during the weight transfer, which delivers most of the weight to the front foot. That shift is instrumental in generating the power that has enabled McIlroy to average 306.2 yards on his drives this season.

Richie Ramsay, a three-time European Tour winner from Scotland, tore ankle ligaments in December 2013. On Monday, he wrote on his Twitter account that the injury “takes longer than you think” to heal.

He also wrote, “Three months till I played after tearing ligaments, and even then getting my foot to work the right way was tough.”

Dr. Kenneth S. Jung, a foot and ankle surgeon at the Kerlan-Jobe Orthopaedic Clinic in Los Angeles, said he would usually tell a pro athlete with a Grade 3 sprain to be prepared to be sidelined for at least four weeks.

“But everyone responds differently,” Jung said in a telephone interview.

The British Open starts in 10 days, a time frame that “definitely makes it a challenge,” he said.

Even if McIlroy is able to play, Jung said, “he’s not going to be pain-free.”

The tricky part with golf, he added, is that players usually have to negotiate uneven terrain during their rounds, even if they find every fairway, and they have to be prepared to walk four rounds with little recovery time in between.

If McIlroy comes back too soon, there is always the chance that he will further destabilize the injured area. Steven K. Neufeld, an orthopedic surgeon with the Centers for Advanced Orthopaedics, emphasized that a ruptured or torn ligament would typically heal without any lingering effects, “but it has to be allowed to heal and rehabbed properly,” he wrote in an email. “And it must be protected for at least eight weeks while it is healing so it doesn’t get reinjured.”

Neufeld, a clinical instructor in the Georgetown University orthopedics department who specializes in foot and ankle surgery, said he would be surprised if McIlroy were able to play the British Open.

“I would give it less than a 50 percent chance that he’ll be comfortable enough to play,” Neufeld said.

It is left to McIlroy to decide how much pain he can tolerate and whether the potential short-term gains of trying to defend his titles in the next two majors are worth it.

Read more here