World No. 1 golfer Rory Mcilroy poses on crutches and with his left leg in a medical support. McIlroy ruptured a ligament in his left ankle while playing soccer less than two weeks before the start of his British Open title defense. (Rory McIlroy via AP/Associated Press)

At the pinnacle of golf, two names stand above all others: Rory McIlroy and Jordan Spieth. They own the top two spots, respectively, in the world rankings, as well as the sport’s last four major titles.

Some 10 days from now, they were to square off in the British Open on the Old Course at St. Andrews, with McIlroy seeking to defend the claret jug and Spieth gunning for the third leg of golf’s elusive Grand Slam.

The news Monday that McIlroy has suffered an ankle injury while playing a game of pickup soccer with friends at his Northern Ireland home has altered the landscape atop the sport. With McIlroy’s status for the Open Championship questionable at best, Spieth may have just lost the biggest threat to his Grand Slam hopes, while the next tier of golfers may not have to worry about the world’s No. 1 player making a seemingly inevitable charge to the top of the leader board.

McIlroy, 26, broke the news on his Instagram account Monday morning — posting a picture of himself on crutches, his left leg in a boot, with an explanation that read, in part, “Total rupture of ATFL (ankle ligament) and associated joint capsule damage. . . Continuing to assess extent of injury and treatment plan day by day. Rehab already started. Working hard to get back as soon as I can.”

In layman’s terms, McIlroy appears to have suffered a badly sprained ankle. The ATFL refers to the anterior talofibular ligament, the one most commonly sprained.

While a spokesperson for McIlroy quickly released a statement saying he still hopes to play in the British Open, he has already withdrawn from this week’s Scottish Open — a key tuneup event — and with the first round of the Open slated for July 16, such a recovery seems unlikely for an injury that typically requires a rehabilitation of several weeks and sometimes requires surgery. The better question may be whether McIlroy can make it back in time for next month’s PGA Championship.

“We will all miss you @TheOpen next week my friend,” tweeted Spaniard Sergio Garcia, McIlroy’s Ryder Cup teammate. “Fast and healthy recovery.”

Paul McGinley, Europe’s Ryder Cup captain in 2014, told RTE Sport, an Irish Web site, that the prospect of having McIlroy miss the Open would “be a blow not just for Rory but a blow for the game as a whole.”

While various medical experts have estimated McIlroy’s chances of playing in the British Open anywhere from 10 percent to 25 percent, Melvin Deese, an orthopedic sports surgeon who once repaired a similar injury to Davis Love III, gave McIlroy a “50-50” chance.

“Could he do it?” said Deese, who was not familiar with the specifics of McIlroy’s injury. “The answer is yeah, he could. Is it wise? Probably not wise. But these guys can block out a lot more [pain] than the average golfer. But if his doctor thinks he can swing without [having surgery first], the operation is going to be the same now as it is then.”

Deese based his “50-50” prognosis on an assumption that an elite athlete has a stronger will and higher pain threshold than the average person and cited the example of Tiger Woods limping his way to the 2008 U.S. Open title on a left knee that required surgery to repair a torn ligament afterward.

“He’s a dedicated guy,” Deese said of McIlroy. “He could probably [play] if that’s what he chose to do it. That doesn’t mean he’s going to perform at his highest level.”

McIlroy is in the midst of a season marked by inconsistency, featuring wins at the Dubai Desert Classic, the WGC Match Play and Wells Fargo Championship, plus top 10 finishes at the Masters (fourth) and U.S. Open (tie for ninth), but also three missed cuts in a three-month span this spring.

Last year, he went wire to wire in winning the British Open at Royal Liverpool , then added the PGA Championship at Valhalla a month later, joining Bobby Jones, Jack Nicklaus and Woods as the only golfers with four major titles before the age of 26.

The last time the British Open was held at St. Andrews in 2010, McIlroy, 21 at the time, overcame a second-round 80 and finished tied for third.

For Spieth, the 21-year-old Texan threatening to overtake McIlroy atop the world rankings, the potential loss of his top rival makes the pathway to a third straight major easier to envision. In winning the U.S. Open three weeks ago, Spieth fought off the charges of several top golfers, including McIlroy, who closed with a 66 to make things interesting down the stretch, and current world No. 4 Dustin Johnson, who had an eagle putt on the 72nd hole to win the tournament but three-putted to lose by a shot.

But in the post-Woods era of championship golf, the best thing the sport had going for it was the prospect of a Spieth-McIlroy rivalry — with a showdown at St. Andrews, the renowned “Home of Golf,” a particularly anticipated chapter. With McIlroy on the mend, that rivalry may be on hold until further notice.

Staff writer Adam Kilgore contributed to this report.