Why Rory McIlroy's driver may have violated PGA Championship rule as history repeats

might have narrowly made the cut at the , but he had to do it without his favoured driver. The Northern Irishman teed off as the pre-tournament favourite at Quail Hollow, but was left fighting to simply make the weekend after a roller coaster second round.

McIlroy began the day three-over-par and, at one point, appeared to be charging as he reached one under after 10 holes. His progress stalled, though, and he eventually carded a 69 after six birdies and four bogeys. That left him one-over-par, meaning he survived by just one shot, but is still nine back from leader Jhonattan Vegas.

However, it has emerged that the 36-year-old before his first round on Thursday. CBS Sports reported that his regular driver was deemed 'nonconforming' after tests by the USGA.

The sanction was due to the worn-down carbon face of McIlroy's Qi10 club. This can occur if a driver has been used frequently, and the more the face flexes on impact, the more head speed that can be generated.

McIlroy has been using his current driver since the start of last year. Officials have now judged it to be producing a 'Coefficient of Time' (CT) that is too high. The higher the CT, the faster the ball will come off the face, which potentially increases distance off the tee.

McIlroy is deemed one of the fastest and most powerful players on the tour, meaning the life cycle of his drivers is likely to be shorter than most. Indeed, it's not the first time the Grand Slam champion has fallen foul of the regulations.

He was also forced into a late change at the Players Championship in TPC Sawgrass two years ago. Rival Xander Schauffele suffered the same fate at the 2019 .

Regardless, the world No.2 has been in no mood to discuss the controversy or his performance at Quail Hollow. After both rounds, he's headed straight off the course after declining to speak to the media.