Graeme McDowell has claimed that Rory McIlroy is suffering from fatigue due to his relationship with tennis star girlfriend Caroline Wozniacki.

The 23-year-old finished 40th at The Masters and missed the cut at the US Open before labouring to joint 60th in the British Open last week.

McDowell believes that travelling around the world to spend time with the Dane is taking its toll on McIlroy's game.

"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. "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].

"Yes, his performance in the big events this year have not be really up to his standard, 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. 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 is currently ranked number three in the PGA rankings.