Graeme McDowell and host Gary Williams on Morning Drive. Rory McIlroy’s globetrotting romance with Danish tennis star Caroline Wozniacki is “wearing him down” according to fellow Northern Irishman Graeme McDowell.

Since he rose to world No 1 in March, McIlroy has been highly erratic and performed poorly in the majors - sandwiching a missed cut in his US Open defence between a share of 40th in the Masters and joint 60th place in last week’s British Open.

McIlroy denies that one thing has led to the other - after all, he racked up a string of wins and made it to world No 1 with the talented Dane by his side.

But while McDowell is backing his Ryder Cup partner to bounce back to form quickly, he believes that jetting around the world to be by Wozniacki’s side as often as possible has taken its toll on him physically.

“There’s no doubt, all the travelling is wearing him down a little bit and we are seeing a little bit of fatigue,” McDowell said on the Golf Channel yesterday as he co-hosted the Morning Drive show.

“But he’s a fit kid and he’s a young kid and he has all the talent in the world. It is only a matter of time [before he comes back].”

Following a spectacular start to the season which saw him become Irish golf’s first world No 1, McIlroy has missed four of his last seven cuts and performed poorly in the majors.

“Yes, his performance in the big events this year have not be really up to his standard,” McDowell said. “But he is going through a little bit of a voyage of discovery right now - for all the right reasons.

“He’s very happy with his personal life and Caroline is a great girl. He will be okay.”

Wozzilroy goes Olympic. Wozniacki and McIlroy in London on Thursday.Asked if he sensed that McIlroy was feeling the burden of expectation since becoming world number one earlier this year, McDowell said: “A little bit. It’s probably his own expectations more than anything.

“He’s had a tough 12 months. Let’s be honest, the boy’s in love. He’s crazy about her. It’s not a bad problem to have.”

McIlroy and Wozniacki, who have styled themselves as Wozzillroy, met for the first time at the world title fight between David Haye and Wladimir Klitschko in Hamburg just over a year ago .

Despite their demanding schedules, the pair have spent as much time together as possible since with McIlroy doing the bulk of the travelling.

Wozniacki rose to world No 1 for the second time last year but has since fallen to No 8 in the WTA rankings, losing in the third round of the French Open and the first round of Wimbledon.

Yet McDowell believes that McIlroy’s determination to be at his girlfriend’s side has taken a physical toll on the 23-year old Holywood star.

“Caroline is obviously got a huge job on her own hands with regard to her tennis and it’s hugely intense,” McDowell said. “She can’t really travel because of her entourage.

“It’s not like Rory, who can be anywhere in the world and all he needs is a bag of practice balls and he can practice anywhere.

“Caroline has her entourage with her - her folks, her hitting partner, her coach - and her travel schedule has been a lot different from Rory’s.

“She can’t really be as flexible with her travel which means when Rory holes that finishing putt on a Sunday afternoon, he’s pretty much jumping on a flight to be where she is.

“That something that he acknowledges is something that just has to happen in the short term because of her career.”

When McIlroy became world No 1 following the Honda Classic in March, he jetted straight from Florida to New York to watch Wozniacki play an exhibition match at Madison Square Garden.

At Wozniacki’s request, he ended up getting out on court to trade shots with Maria Sharapova and flew on to Miami, where he finished third in the WGC-Cadillac Championship at Doral.

Since then his form has been erratic, however, and after losing and then regaining the world No 1 ranking, he lost it to Luke Donald when he missed the cut at the BMW PGA Championship in May.

Following his disappointing performance in the Open, he was relegated to world No 3 behind Donald and Tiger Woods in the latest rankings and while he confessed at Royal Lytham that he had lost some confidence in his swing, he will have high hopes of a strong finish to the season.

He faces seven events in the next nine weeks, starting with the WGC-Bridgestone Invitational in Akron next week and the following week’s US PGA before the FedEx Cup series and the Ryder Cup.

He’s unlikely to see much of Wozniacki during that time, though he has been by her side this week as she prepares for the Olympic Games in London.

The celebrity couple were pictured together under the Olympic rings in the athletes’ village with McIlroy tweeting: “Unbelievable experience in the athletes village with @CaroWozniacki.”