Even the longest Indian summers must turn to autumn eventually.

For years, Tom Watson's steadfast refusal to go gently into golf's good night has been one of the sport's most compelling narratives, but at the age of 64 he seems finally to be accepting that you can only rage against the dying of the light for so long.

That much was clear as Watson sat down to talk at Gleneagles last Tuesday. Given his hectic schedule of Ryder Cup "Year to Go" events over the preceding 48 hours, the man from Kansas City actually looked improbably fresh, but Watson soon volunteered the admission that the same could certainly not be said of his golf game anymore.

Watson, of course, established himself as the sport's most celebrated senior at Turnberry in 2009 when, two months short of his 60th birthday, he came agonisingly close to adding a sixth Open Championship title to the five he had won between 1975 and 1983. Nor was it a one-off, as he secured top-30 finishes at both the Masters and US Open the following year.

But having played Canute -rather more successfully than the original - to the tide of time for so long, the water is now lapping round his ankles. "I haven't played well lately, which is a disappointment and continues to be a disappointment," Watson sighed. "I see the horizon getting closer to the time when I'm going to have to hang it up. And I don't relish that fact. I don't like it, because this is what I do. I'm a professional golfer."

With his Prairie Home Companion drawl, Watson has a way of making every utterance sound like an epilogue, but this one is for real. His Open exemption runs out at next year's tournament at Hoylake, after which his captaincy of the US team at Gleneagles, just a couple of weeks after his 65th birthday, is already starting to look like a potential swansong.

That it takes place in Scotland must make that grand exit all the more inviting to Watson, whose fondness for the place is well documented. "It might be," he said when that suggestion was aired, but nothing is certain yet.

"It just depends," he elaborated. "I go back to my ability to play. If I can't play competitive golf the way I think I have to then I'll hang it up. I don't know if I'm going to be a hanger-on, telling myself that I can still do it.

"You get to that time when you say 'I'm playing pretty good, I'm going to go out and play again'. Usually that doesn't work. I don't think it has ever proven to work. But it's hard to give it up. So I don't know how I'm going to end my career. But I've been thinking about it. It's getting closer and you have to prepare for the future. You just can't let it happen. You can't just say 'I'm done. Now what do I do?' You have to be prepared."

Maybe so, but it would be wrong to suggest Watson has slipped seamlessly from being one of golf's most feared competitors to being the sport's favourite avuncular old cove, good for nothing but the odd snatch of homespun wisdom. He can dish up the folksy aphorisms all day, but in a year's time he will still have to lead his US team into the cauldron of what is already looking likely to be a titanic Ryder Cup contest. At which point, bumbling along like an extra from Still Game is probably not what will be required. Some likely members of next year's US team had yet to draw their first breaths when Watson was in his Major-winning pomp, which begs an interesting question. Did he think his credibility as a competitor had been levered up by what he did at Turnberry four years ago?

Watson smiled. "I think, possibly, it might," he replied. "I scared those kids. I scared them.They looked at me and said 'Who's that old guy? He's not supposed to be here. Can he still play like that?' I got some street cred with the younger players, I certainly did. And maybe it helped make the decision by the PGA to ask me to be Ryder Cup captain."

Twenty years have passed since Watson led the USA to a 15-13 win over Bernard Gallacher's European side at the Belfry. In which time, no American captain has been able to match his feat of winning on this side of the Atlantic. The record ­troubles Watson. A few weeks ago, he called up Roy Williams, the celebrated college basketball coach, for tips on winning away from home. The advice was to forget about gameplans. "I coach by the seat of my pants," Williams said.

Watson will do the same, and will have no compunction about dropping big-name players who are not delivering points. Watson has criticised aspects of Tiger Woods' life in the past, and he is unlikely to be impressed by the world No 1's Ryder Cup record of 13 wins, three draws and 17 losses. "It's what I did in 1993, and I will continue to do it," said Watson when asked about ditching the stars. "We're there to win. There are going to be situations when the dynamics of the game change. The key is, can you make those decisions in the heat of the battle, can you make the right decisions? Not emotional decisions, but the best informed decisions. That's the key to being a good manager and the key to being a good captain."