Rory McIlroy has hit back at criticism of the challenging rough at Erin Hills as the Wisconsin course prepares to host the US Open for the first time this week.

Thick, calf-deep fescue grass bordering the fairways at the rugged course have been described as unplayable, with golfers posting videos and images on social media warning of the difficulties of hitting the rough.

But world number two McIlroy, who arrived in Wisconsin on Friday to survey the course as he chases a fifth major title, was unimpressed on Tuesday after being informed that the fescue was being cut back on certain holes, despite the large fairways.

"Really? We have 60 yards from left line to right line on the fairway," McIlroy told reporters.

"You've got 156 of the best players in the world here, if we can't hit it within that avenue, you might as well pack your bags and go home.

"These are the widest fairways we've ever played in a US Open. "Even the first and second cut is another ten yards on top of that. So if you've got 50 or 60 yards to hit into and you're complaining about the fescue that's wider than that, I don't think that's an issue."

A Facebook video posted by golfer Kevin Na on Sunday went viral.

The video showed Na throwing a ball into the fescue from three feet which promptly vanished.

When the American discovered the ball he whiffed at his first attempt, and then hacked it only a few feet on his second attempt.

Na later insisted he had not intended the video as a criticism of US Open organisers but had merely sought to demonstrate that the fescue was "a little overdone."

"All I was trying to show was the fans was an inside-the-ropes view of what we're dealing with," Na said.

McIlroy however was having none of it.

"I get that it's thick and whatever, but it's a hazard," he said.

"If you put red lines just right along that people wouldn't complain, it's a hazard. It's a US Open, it's supposed to be a tough test. And if guys can't put it into play within a 50-yard zone I don't think they've got much to complain about," he added.

The 28-year-old Northern Irishman meanwhile said he has no concerns with the rib injury which has bothered him recently as he hunts for a second US Open title this week following his breakthrough 2011 win at Congressional.

McIlroy revealed he hopes to take a more relaxed approach into Thursday's opening round in an attempt to recapture the sort of form which saw him scoop all four of his major wins between 2011 and 2014.

"Over the past couple of years the first round of majors I've been a little bit tight and a little bit tentative," he said.

"I need to get away from that because that's not how I play my best golf.

"That's why I like this golf course, it allows you to be aggressive and swing freely and get after it.

"I feel like if you prepare 100 percent the right way, mentally that puts you in a great frame of mind to go out there and attack the golf course. So that's what I've tried to do this week, and hopefully it pays off."