Rory McIlroy could miss next week’s Open Championship and face a lengthy lay-off after suffering a serious ankle injury playing football.

The reigning Open champion has pulled out of this week’s Aberdeen Asset Management Scottish Open after sustaining a “total rupture” of a ligament during a “kickabout” with friends on Saturday.

The 26-year-old has not ruled out trying to defend his title at St Andrews, but his participation is in doubt after he posted a picture of himself on crutches and wearing a protective boot.

The full extent of the problem is not yet known. It is understood the Northern Irishman has been scanned, but a full prognosis may not become clear until later in the week when swelling has had time to go down.

He is currently in Northern Ireland and being assessed by his medical team, which includes experienced physio and sports scientist Dr Stephen McGregor.

McIlroy wrote on Instagram: “Total rupture of left ATFL (ankle ligament) and associated joint capsule damage in a soccer kickabout with friends on Saturday. Continuing to asses extent of injury and treatment plan day by day. Rehab already started...working hard to get back as soon as I can.”

Recovery from such injuries in athletes, if as severe as McIlroy has suggested, can take months or even require surgery. The fact the injury is to the left ankle is also significant for a right-handed player as that joint bears most of the pressure through the swing.

McIlroy, who won the Claret Jug at Royal Liverpool last year, was the favourite for this year’s event, which begins on July 16. Much had also been made of a potential rivalry with Jordan Spieth, winner of the year’s first two majors.

The world No.1’s form has been mixed this season, but he was on the fringes of contention at both the Masters in April and last month’s US Open at Chambers Bay, finishing four and five strokes respectively behind Spieth.

He was due to play a the Scottish Open at Gullane, which starts on Thursday, to prepare but the European Tour has confirmed his withdrawal.

Championship director Peter Adams said: “Naturally the news on Rory having to withdraw from the Aberdeen Asset Management Scottish Open is very disappointing for the tournament.

“Any tournament which loses the world No.1 through injury is going to be affected, but we are still looking forward to hosting one of the strongest fields in Scottish Open history at Gullane. We wish Rory as speedy a recovery as possible.”

McIlroy is not expected to make an announcement on his possible participation at the Open until next week at the earliest but fellow professional Richie Ramsay fears the worst.

The Scot tweeted: “I had a full tear of ligaments in my ankle not long ago. It takes a lot longer than you think to heal. Three months til I played after tearing ligaments and even then getting my foot to work the right way was tough.”

Should McIlroy be sidelined and be out of action for more than a month, he would also be doubtful for the US PGA Championship, the year’s final major and another title he currently holds.

Meanwhile, Spieth does not believe McIlroy's anticipated absence from the Open will make his life at St Andrews any easier.

The 21-year-old Texan, who learned of the Northern Irishman's injury through social media, would prefer his rival to be in action at the Royal and Ancient Golf Club.

"For me, it doesn't change anything," he said. "It's still just as challenging. It's still a major championship and there is a lot of unbelievable talent. I obviously wish he was there.

"It kind of dampens it. You want the defending champion, much less the best player in the world at the event.

"You want all fields to be full strength no matter who it is. Losing the number one player in the world for a major championship would be tough."

Recalling the moment he first saw the Instagram picture which featured McIlroy on crutches following a footballing mishap, Spieth added: "I thought it was really unfortunate. Accidents happen, and I just wish for a speedy recovery. We all want him back as soon as possible."

Paul McGinley, McIlroy’s captain at last year’s Ryder Cup, heard the news as he visited Wimbledon on Monday and expressed disappointment at the prospect of him not featuring at St Andrews.

McGinley said: “I’m sure he’ll be very disappointed. I know St Andrews is a golf course he loves and a golf course that really suits his game. It’s a shame for the tournament and a shame for Rory.”