Tom Watson has urged Rory McIlroy to cut out the "cancer" which is hampering his efforts to add to his four major titles.
The 32-year-old Down man suffered a frustrating US PGA Championship campaign last month, failing to break par in any of his four rounds at Kiawah Island as his wait for a fifth success extended to 24 major championships since his own PGA success at Valhalla in 2014.
Asked what he needed to do return to contention, eight-time major winner Watson told the PA news agency: "I just think he needs to find that winning golf swing, or that belief in his golf swing, that he needs to win.
"Sometimes you have a slight doubt and that doubt grows as a cancer, and you've got to eliminate that cancer, that thought that 'I just don't have it this week'."
Watson knows from his own experience that sometimes it takes an ability to scramble for a player to play himself back into form and that requires a solid short game.
He said: "You need to be able to rely on your short game. I could rely on my short game, the up and down. When I wasn't playing well... I won a number of tournaments in my career when I wasn't playing particularly well.
"I won an Open Championship there at Birkdale in '83. I wasn't playing particularly well, but I had a strategy to play the golf course and I made the putt at 16 in the final round and it put me in position to win.
"I missed the landmines. I played number six and Birkdale properly, I missed the landmines and kept myself just the leader of the pack.
"That's what Rory has to do. He has to go in there and find something that's going to give him the confidence that 'Yeah, I've got it now', a light switch goes on in the golf swing."
Watson has warned Phil Mickelson will be a force to be reckoned with at this summer's Championship after striking a blow for golf's fifty-somethings.
Mickelson became the game's oldest major winner last month when he claimed the 103rd US PGA title at Kiawah Island at the age of 50.
"You look at what Phil Mickelson did at age 50. I've always contended that you don't stop winning on the PGA Tour or the regular tours against the kids, you don't stop winning in your fifties, you can still win in your fifties.
"It hasn't happened very often, but you can still win. You've got your strength - Phil still hits the ball a long way and can compete against those kids; I could hit the ball a long way in my 50s and still compete.
"If you keep your focus and trying to be the best into your fifties, you can still do it.
"He's got a great short game. If he can miss the landmines, which are the bunkers - you don't hit the ball in the bunkers off the tee. If you hit the ball into the bunkers of the tee, it's like hitting it into a water hazard. It's a stroke penalty.
"If you can avoid those landmines and you're putting pretty well, you can win in links golf."
"It does still sting. I had the opportunity. When I birdied the 17th hole and playing 18 right down-wind, it was, 'I may have this'.
Watson, who was speaking as the R&A launched a ticket ballot for next year's 150th Open Championship at St Andrews, famously came agonisingly close to winning the Claret Jug as a 59-year-old at Turnberry in 2009, ultimately losing to Stewart Cink in a play-off.
Almost 12 years on, he admits the near miss still hurts.
He said: "It does still sting. I had the opportunity. When I birdied the 17th hole and playing 18 right down-wind, it was, 'I may have this'.
"The iron that I hit was as well as I could hit it and it just didn't stop. It caught a gust of wind and it just trickled over the green - and I screwed up."
Watson's five Open titles came during a remarkable eight-year purple patch between 1975 and 1983 at Carnoustie, Turnberry, Muirfield, Royal Troon and Royal Birkdale, although never at St Andrews, where he was runner-up to Seve Ballasteros in 1984.
Only Harry Vardon has more victories, although Watson modestly insists he has played only a small part in the Championship's glorious history.
He said: "I'm a small part of the history, I agree with that, but there's Harry Vardon, there's Young Tom Morris at the beginning of the Open Championship, there's of course Bobby Jones and Jack Nicklaus and Tiger Woods and Arnold Palmer, there's probably the greatest links player ever, Peter Thomson, who won five times.
"We all accented the history of the Open Championship and it knitted a very rich cloth, I guess you might say, to the history of the Open Championship."