Four-time major champion Rory McIlroy has lambasted US Open competitors complaining about long rough at host venue Erin Hills.

The 7,100m Wisconsin golf course features knee-high fescue grass in the primary rough but was mowed back in some areas on Tuesday after US PGA Tour players, including Kevin Na and Wesley Bryan, expressed their disdain for the penal grass.

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On Monday, Na was particularly critical in an Instagram video, during which he demonstrated how the ball did not escape the rough despite hitting two shots.

In a video titled Be careful at Erin Hills, Bryan walked two paces off the fairway and dropped his ball into the fescue.

The ball all but disappeared as Bryan said the "stuff's about two feet tall".

But 2011 US Open winner and world number two McIlroy said his peers should be happy with "the widest fairways" he has seen in his nine US Open starts.

The 28-year-old Northern Irishman blasted the cutting back of up to 10 yards of fescue rough on some holes.

"Really? We have 60-yard fairways from left to right. These are the widest fairways we've ever played in a US Open. Even the first and second cut [of intermediate rough] is another 10 yards on top of that," McIlroy said on Tuesday.

"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."

Lee Westwood also took to Instagram, posting a comical video of his caddie Billy Foster emerging from the long grass, leopard-crawling while exclaiming, "I found it!" with a golf ball in hand.

A clearly frustrated McIlroy claimed the wider fairways lessened the potency of his world-class form with the driver.

He ranks second on the US PGA Tour for strokes gained off the tee and fifth in driving distance, with an average of 308.5 yards.

"I don't think it's a secret that I feel like my driver is one of my biggest weapons," McIlroy said.

"If I can get it in my hands more regularly, and I think if the field has to hit driver more often, that plays into my hands, too."

McIlroy has been under an injury cloud since fracturing his rib in January, forcing him to spend seven weeks on the sidelines recovering.

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The ailment flared up again during the Players Championship in May and an MRI scan on his rib prompted McIlroy to miss three events leading into the US Open.

He rubbished suggestions a lack of tournament play affects his US Open preparation, pointing to his tie for seventh upon his return to golf in March at the World Golf Championships, in Mexico, and another top-10 at the Masters a month later.

"I opened up with 68 in Mexico coming off the injury and I took a lot from that," he said.

"I don't feel like I need a run of events to get back into it. I feel like I can pick up confidence pretty quickly."

Since winning the US Open in 2011, McIlroy has only recorded one top-10 and one top-25 in five starts at the event.

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AAP/ABC