Russell Knox admits he is desperate to win the FedEx Cup to prove he should have been given a Ryder Cup wild card ahead of a player rated in the same league as Tiger Woods and Rory McIlroy.

Knox was overlooked by Europe captain Darren Clarke despite missing out on automatic qualifying by a single place and being ranked 20th in the world, comfortably higher than Clarke's choices of Thomas Pieters, Lee Westwood and Martin Kaymer.

Clarke admits telling Knox he had missed out was one of the toughest moments of his career, but believes Pieters has the ability to win major championships and become world number one.

"I said all along I would not pick a rookie, I would be reticent to do so," Clarke said. "But he (Pieters) just brings something special. He hits it so far and his short game is fantastic.

"I've been on tour for a long time and I've seen massive talent come along. I played with Tiger when he was an amateur at the 1996 Open. I've seen Rory up close since he's been a very, very young kid. Thomas Pieters impresses me in the same league as those guys. He has that amount of talent."

Knox is currently seventh in the FedEx Cup standings on the PGA Tour - Henrik Stenson is the next highest European at 21st - and therefore in contention to win the overall title and $10million bonus at the Tour Championship, which finishes just five days before plays gets under way at Hazeltine.

"It's certainly motivated me for the next three weeks, that's for sure," said the 31-year-old Florida-based Scot. "I have to use this as a springboard to try and win the FedEx Cup. I've never wanted to prove someone wrong so badly in my life I think.

"It's not sour grapes or anything. Darren had an extremely difficult decision and all of those three guys were worthy of a pick.

"When Darren called me it was obvious within one second that is wasn't going to be good news. It was a very short phone call. I didn't feel like I needed to ask any questions or give my opinion on anything. It was obvious that he had made up his mind and that was final. I respected his decision.

"I was very disappointed not have gotten the nod. But I'll use this as motivation over the next three weeks."

Clarke admitted he had wanted Knox to play in the Wyndham Championship a fortnight ago to try to qualify, but that Knox wanted to be "fresh" for the FedEx Cup.

"I hope the decision not to play Wyndham ultimately had nothing to do with it, maybe it did, but I'm sure no one will ever talk about that," Knox added. "I'm happy with the decision I made, I felt it was the best one for me and I don't think it would have made a difference anyway.

"It's going to be difficult for me to watch (the Ryder Cup) but I probably will and I'll be rooting for the team of course. I wish them all the best and hope they win.

"Of course I feel like I deserve to be there and should be playing but I'm not, so I have to respect the decision that's been made. Every year there's a guy in my position that doesn't get picked and it's a story right now, but in a couple of week's time when it all starts, I'm sure it'll be forgotten that I'm not in the team."