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The players explain why the rough at Oakmont golf course could make this one of the hardest U.S Opens in history.

Tiger Woods famously said a 10-handicapper would not break 100 at Oakmont, but what are the world's leading players saying about one of the world's toughest courses ahead of the US Open?

Jordan Spieth, defending champion

"You can't let your mind slip on these greens for one moment, or else you're going to be left with possibly a 10- to 15-footer on the next putt, if not worse. So you really have to be cautious of it. I think they putt very similar to Augusta and, at some places, are more severe. 

Jordan Spieth is wary of the slick greens

"It's extremely challenging, where par is a great score, but if you hit the ball where you were looking, you could have birdie opportunities on quite a few holes. But at the same time, I'd sign for even par. I don't think anyone's going to be in the red come 72 holes. So it will be a challenge, but I'm certainly looking forward to it."

Rory McIlroy, 2011 winner

"I would expect the more established players and those up near the top of the world rankings to do well this week, because it is a golf course that can separate the players that are playing well from the players that are just slightly off their games. The guys that are struggling, it will really magnify that weakness and you'll see a lot of high scores.

Rory McIlroy believes there is pressure on every shot

"It's a great test of golf. Every shot you hit, you're under pressure to hit a great shot because you can't really miss it. And if you get your ball on the fairway, you've just got to make sure that you leave yourself below the hole on the greens. And even in some cases, that may mean missing the green.

"You could go a whole round here without hitting it at any pin and just trust that where you're hitting it into is the best leave. I'd much rather have a 30-foot putt up the hill on these greens than even an eight-footer down the hill."

Jason Day, world No 1

"This year, we've got tough rough. The greens are tough. Practically the whole course is tough. You've just got to go with it and try and play your best and hope for the best sometimes - attitude is huge. You have to come in with a positive attitude, regardless of what the outcome is.

It's all about having the right attitude, according to Jason Day

"If you're going to have a bad attitude, you may as well not even tee it up because you probably won't play good anyway. That's just one less person you have to worry about at the end of the week."

Ernie Els, Oakmont winner in 1994

"This is going to test the boys this week, I promise you. Of the four rounds you're going to play, at least one - maybe two - is going to be a survival test. You breeze through four rounds here with you having your way with the golf course, you're going to win by quite a few golf shots.

Ernie Els is predicting a test of survival

"You're going to have stretches where you're going to have to try and survive, and it's going to happen to every player in the field. That is why this is the ultimate US Open test at Oakmont."

Danny Willett, Masters champion

"I think it gives you a lot of options off the tee depending upon how aggressive you want to play, but then you have to be really careful on where you place your ball around the green. A lot of golf courses you pitch up to and everybody is hitting a driver here, a two-iron down this hole.

Masters champion Danny Willett insists Oakmont 'gives you a lot of options'

"This course gives you a lot of options depending upon how aggressive you want to be, depending upon how comfortable you are of either laying back off the tee or trying to get a wedge in your hands and trying to spin out with these firm greens."

Justin Rose, 2013 winner

"They probably are the toughest greens in golf based upon the fact that just off the green you have very, very thick rough. And when you're pitching to the green out of very, very thick rough, it's very unpredictable how the ball is going to come out exactly.

Justin Rose labelled the greens as the toughest in golf

"Augusta National, I would say the greens are just as severe, but you have a little bit more control on the ball at all times. You're playing out of out of the short grass and it's more predictable. So the combination of both of those makes it incredibly tough.

"I think that there was talk of the greens rolling 16 or something on Sunday or Monday, which was probably a test. The greenskeepers and whatever trying to figure out how far they can push them and where they're at. Obviously, those sorts of numbers are unheard of really. It's obviously fun to play. You've got to relish that sort of attitude anyway."

Rickie Fowler, world No 5

"I don't think you can play enough rounds here to really know it. But these are some of the craziest greens I've ever played and most penal fairway bunkers I've entered, and I'm trying to stay out of those as much as possible this week. It's a fair golf course. You've just got to be on the right side of the hole and you've got to drive the ball well.

Rickie Fowler believes the greens are the craziest he's seen

"A lot of characteristics of a typical, tough and hard US Open. Ball striking is going to be key this week, playing well tee to green. I don't see many putts being made, but it will be a bonus if you're able to roll a couple in."

Branden Grace, tied fourth last year

"I had a putt on the 13th hole on my first practice day on Sunday. I hit a six-iron to 15 feet, pin was middle front right, and I hit it 12 feet, 15 feet past left, and I was dead. I couldn't keep it inside 20, 25 feet.

Branden Grace could find himself aiming for bunkers

"So a lot of times, it's better going straight for the pin. Sometimes, you might actually even hit it into a bunker to give yourself the best chance if you're in trouble."