Rory McIlroy admits there are still "learnings" to take after he missed his first cut at the RBC Canadian Open on Friday since the Open at Royal Troon last July.
The Holywood man carded a quadruple bogey, a double and four other bogeys in an eight-over-par round that left him languishing 21 shots behind halfway leader Cameron Champ and admitted his "concern".
McIlroy was hoping for more ahead of next week's US Open and felt the new driver choice was going to solve the issues off the tee that began when his club was deemed 'non-conforming' in a random check at the PGA Championship earlier this month.
"Of course it concerns me. You don't want to shoot high scores like the one I did today," he said.
"Still, I felt like I came here obviously with a new driver thinking that that was going to be good and solve some of the problems off the tee, but it didn't.
"Going to Oakmont next week, what you need to do more than anything else there is hit fairways. Still searching for the missing piece off the tee.
"Obviously, for me, when I get that part of the game clicking, then everything falls into place for me. Right now, that isn't. Yeah, that's a concern going into next week."
Despite his concern going towards Oakmont, the Masters champion still believes he can take something from the somewhat disastrous second-round 78, where he only managed to find four fairways.
"I think there's still learnings that you have to take from a day like today," he said.
"I'm gonna have to do a lot of practice and a lot of work over the weekend at home to try to at least have a better idea of where my game is going into next week."
McIlroy revealed that missing the cut will allow him to test different drivers and adds that he will prioritise speed off the tee over hitting fairways, which may be a tactic carried into the US Open if the issues can't be remedied.
"I went back to a 44-inch driver this week to try to get something that was a little more in control and could try to get something a bit more in play.
"But if I'm going to miss fairways, I'd rather have the ball speed and miss the fairway than not.
"I said to Harry (Diamond, caddie) going down the last, this is obviously the second time this year I've tried the new version [of driver], and it hasn't quite worked out for me.
"I'd say I'll be testing quite a few drivers over the weekend."
