Mahan finished one spot shy of automatic qualification for the 12-man lineup, and was then overlooked by US captain Davis Love III who chose Dustin Johnson, Jim Furyk, Brandt Snedeker and Steve Stricker as his final selections.
"The Ryder Cup has been a goal for every American player, and it's disappointing not to be a part of it," Mahan told reporters while preparing for this week's BMW Championship in Carmel, Indiana.
"I've been part of the last five (US) teams, so it hurts not to be a part of it," he added, referring to both the Ryder Cup and the Presidents Cup. "It feels a little empty right now."
Mahan made his Ryder Cup debut at Celtic Manor in Wales two years ago and was seen as a likely candidate for selection this year after he triumphed twice on the 2012 US PGA Tour.
However, he ended up ninth in the Cup points standings after last month's US PGA Championship at Kiawah Island with only the top eight players booking their places on the US team.
With three more weeks left to advance his claims for a captain's pick, Mahan skipped the Wyndham Championship, missed the cut at the Barclays tournament and tied for 39th at the Deutsche Bank Championship on Monday.
"It's been a good year," said Mahan. "I've played pretty well. Obviously I haven't been playing as well recently, but there are still two (US PGA Tour -) events left ... and they don't feel quite as important as I want them to be right now.
"So I have to work on that this week. That's my goal ... is to find that kind of motivation right now. That's going to be my biggest key this week."
Mahan, who has won five career US PGA Tour titles, conceded his chances of a late Ryder Cup call-up had been slim after he failed to shine in the first two play-off events - The Barclays and the Deutsche Bank Championship.
"I think he (Love) stated he wanted Stricker and Furyk (as wildcard picks), so there were really only two spots left," the 30-year-old Mahan added. "Brandt and Dustin just outplayed me at the end of the day.
"I just didn't play good enough, and that's okay. It's okay to get beat by somebody. That's part of golf, and that's part of the game. But like I say, it just feels empty right now."
Mahan, who clinched the biggest victory of his career at the WGC-Accenture Match Play Championship in February, will tee off with fellow American Matt Kuchar and Spaniard Sergio Garcia in Thursday's opening round at Crooked Stick Golf Club.