"If I train or play now I feel it the day after," he said. "I might just have one last fling left in me, but that's all."
Also having a last fling is the 41-year-old Wigan coach, Graeme West, who last appeared in the first team in 1991, but has played in reserve matches and charity games since then. The former New Zealand international played some rugby union in his teens and his height - he is 6ft 5in - makes him a potential ball-winner in the second row.
At 32, Lydon is no fossil, but nagging knee problems effectively ended his playing career almost two years ago. There have been compensations, like a high-profile job as the public face of the Wigan club, but today's comeback is strictly a one-off.
It is not, however, a sentimental selection. Lydon trained with the first team and they asked him to play against Bath. He has two things to offer - a rugby union pedigree in his youth and a famous long-range kicking game that could be tactically valuable.
Lydon was an England Schoolboy international in union, touring Zimbabwe with the likes of Kevin Simms and facing Rory Underwood in North of England trials before deciding his future lay in league.
"I enjoyed my rugby union and I probably would have carried on with it if better and better offers hadn't come from league. I've no regrets about opting for league, but it's only natural that you wonder how far you would have gone."
For Lydon, now in the middle of a testimonial season after 10 years with his home-town club, that must always remain a matter of conjecture.
His experience in union, he also believes, is too distant to be of any direct benefit today. "It's too long ago," he says. "Even players like Scott Quinnell, who have not been away from union for long, have been finding it difficult to adapt to it again."
That leaves Lydon's celebrated field-gun kicking. "The boot's all right," he says. "It's the leg that's no good."
In fact, observers of Wigan's union preparation say that Lydon's kicking can still earn valuable ground, even if he might have to pay for the privilege on Sunday morning.
He is making no promises, though, that there will be any repeat of his most memorable kicking feat, a drop-goal measured at a Hugo Porta-esque 61 yards in the Challenge Cup semi-final against Warrington in 1989. "I would need a howitzer now to get it over from that range," he said, once more enjoying the role of the pensioned-off dodderer.
For all that, Lydon's cool head can exert a steadying influence in trying circumstances, especially if Shaun Edwards does not make one of his Lazarus- like recoveries and Craig Murdock plays at scrum-half.
But he has no dreams of leading them to victory. "I think it is a false premise to say that because we won the Middlesex Sevens we can beat Bath at the 15-a-side game.
"Even in the Sevens, we struggled at times to get the ball. We were 15 points down in the final before we got hold of the ball and that is a game with a lot more space and a lot less in the way of technicalities."
Wigan have worked hard in preparation - you would expect nothing less of them - but Lydon says that their knowledge is superficial. "It's like cramming for exams. We will be going in knowing that we have not really mastered our subject.
"In the heat of the moment, you tend to go back to what you know and our instincts won't be any good to us at all."
Nor does Lydon delude himself about Bath's likely approach, after the 82-6 hiding they took at Maine Road.
"They've got to win it," he said. "They will start off as though it's a cup final. They will go full tilt for 20 minutes, see how we cope with it and then think about playing open rugby.
"They also realise that we eased off at Maine Road. That was our game we were playing then and we were not in the business of humiliating or injuring people."
Lydon admits to worrying about the potential for injury when two cultures clash in the front rows of the scrum today. "A lot will depend on the referee there, but the priority should be that nobody should get hurt.
"This has all been a great piece of history to take part in, but we have our bread and butter to think of."