“I’m well past that time,” said the Irishman, speaking after finishing joint-fourth in the US PGA Championship, of thinking about doubling up at Whistling Straits in September.
“I'm very much dedicated to being the captain. I'm letting other people have their time. I had mine. And you can't do both.
“Nobody's ever going to be a Ryder Cup captain and a player at the same time. It's a full-time job being the Ryder Cup captain.”
Harrington turns 50 in August, but, on the back of his own performance and also being inspired by Phil Mickelson, he has not given up hope of adding to his three majors.
“There's nothing stopping me in my golf swing,” he said. “I swing the club well enough and I hit the golf ball well enough and I hit it far enough to compete.
“Give me the right conditions and I will be competitive, no doubt about it. We all dream it can happen and we push for that, and it keeps me getting up in the morning.
“I'm not too far away, my major wins came after me seeing some good stuff and being able to build on that, and I do see some good stuff in this week.
“I just need to find that one thing on the putting or whatever and I could be as physically good a player as I ever was, but there's a lot more competition these days.”