Butch Harmon has warned world number one Rory McIlroy that he is in danger of damaging his game by bulking up "too much".

Harmon was commenting after 25-year-old McIlroy released a video this week demonstrating his workout routine, in which he revealed how he has transformed his physique.

"If you look at Tiger [Woods] and how much stronger he got as he went on, you look at Rory the way he is now," Harmon told Irish radio show Off The Ball.

"The only caution I would give Rory is, I see a lot of pictures of him lifting a lot of very heavy weights and I think, in a way, you can almost hurt yourself in the gym if you get too bulky. Hopefully, he will keep his body tone down, more like a Dustin Johnson, who's in absolutely perfect physical shape to play golf"

McIlroy is currently preparing for The Masters, where he will be aiming to complete a career clean sweep of major titles.