World number one Rory McIlroy will be "gutted" to miss out on the defence of his British Open Championship title next week, according to Ryder Cup team-mate Graeme McDowell.
McIlroy revealed on Monday that he had suffered a ''total rupture'' of the anterior talofibular ligament in his left ankle while playing football with friends.
The 26-year-old pulled out of this week's Scottish Open at Gullane and although he initially did not rule himself out of competing at St Andrews, the four-time major winner said yesterday he was taking a "long-term view" of the injury.
The clash between McIlroy and Masters and US Open champion Jordan Spieth had been eagerly anticipated and McDowell said: "It's hugely disappointing, especially with him and Jordan and everything that's going on. It was looking a really exciting Open for all involved.
"I was reading between the lines as to what the description of his injury was. I wasn't expecting him to play in the Open, so I'm not surprised he's pulled out. But it's a massive blow for the tournament, he's the world's number one player. We hope for a speedy recovery.
"No one would love to stop Jordan in his tracks next week more than Rory. With the fun rivalry going on and everything, he's going to be gutted. I saw the golf course last Saturday and I believed that Rory was rightly a favourite. I thought he'd get it done round there."
Former US Open champion Justin Rose added: "I would have been surprised if he was there given the initial diagnosis but it's a big shame for him and the tournament."
McIlroy's defence of the Bridgestone Invitational in a month's time and the following week's US PGA Championship at Whistling Straits is also in serious jeopardy as he 26-year- old could face months on the sidelines.
Andrew Roche, a consultant orthopaedic surgeon at The Lister Hospital in London, said this week: "If it is a high-grade injury, a complete rupture, there would almost certainly be a lot of swelling, a lot of bruising and it would be painful. It could mean three months out of action.''
McIlroy is the first player not to defend his Open title since Ben Hogan in 1954 - Hogan won the Claret Jug at Carnoustie in 1953 in his only appearance in the event.
A statement on the Open Championship Twitter account read: "We are naturally very disappointed that Rory will be unable to defend his title at St Andrews next week.
"Rory will play in many more Open Championships and our primary concern is for his complete recovery. Everyone associated with The Open wishes Rory the very best as he looks to return to full fitness."
Florida-based Scot Russell Knox, who was first reserve, replaces McIlroy in the field at St Andrews. World number 77 Knox learnt of his inclusion while playing a Pro-Am event, ahead of this week's Scottish Open at Gullane to the east of Edinburgh.
"My wife sent me a text out on the golf course saying that Rory had withdrawn but I was waiting for official confirmation from the R&A (The Royal and Ancient Golf Club) but then my manager received an email from the R&A to say 100 percent I am in," Knox said.
"I was down on the 12th hole and had a big smile on my face when I got the text and bizarrely it was close to where I got a hole-in-one some years back.
"Naturally, I am disappointed for Rory as everyone is barracking for Rory as he's in the prime of his career and he would have had a great chance to win at St Andrews.
"Nobody wants to gain because another player is injured, so it is a horrible way to sneak in but I am very happy. I am into my first British Open Championship and can't wait to give it a blast."
The 30-year-old Jacksonville-based Knox has only previously competed in two majors, finishing tied 45th at the 2013 US Open before missing the cut at last year's PGA Championship.
"Now that I know I am into the British Open it's a great weight off my shoulders as it means it will now not be in the back of my mind playing in this week's Scottish Open," he added.