That 15-minute cameo brought up his 355th Football League appearance and his first competitive action since the play-off semi-final defeat to Derby in May, summer surgery on a problematic ankle delaying his 2019/20 season kick-off.
For the 28-year-old, senior enough now to comfortably carry the title of veteran, there were a few butterflies amid the excitement.
“I just couldn’t wait to get back out,” he said.
“I knew I would be on the bench and thought I might get on.
“It’s the type of game where you know it’s going to be tight either way so if we’re winning I might be called on to hold onto the game, or if we’re looking for a goal I might be called on for another option.
“I got told to warm up pretty much the whole first half, the whole of half-time and then I got on. There were a few nerves.
“The boys had been doing really well, I don’t want to come on and mess it up for them or anything.
“The morning of [the match], kind of felt like the first game of the season for me – the first game of every season you’ve got a few nerves.
“Coming on in the West Brom game felt like that for me, a few nerves but once I got my first touch I was fine.”
A trip to Millwall followed, an afternoon that would have presented a stiff enough physical challenge, even before Gaetano Berardi’s 14th-minute red card left Leeds down to 10 men and Ayling on the pitch for a full 90 minutes.
He moved from right full-back to the centre of the defence alongside Ben White and, result excepting, came through fine and was even himself surprised by how well his body coped.
“It was a hard game to come back into from the start, then we went down to 10 men, but I went to centre-half and it’s not as physical as right-back.
“My numbers were still up, I had to run around a lot. We had a lot of the ball but there was still a lot of running in behind for me and Ben [White] to deal with.
“I never cramped up, which is quite unusual for your first game back. I felt good all the way to the end.”
Ayling is honest enough to admit that he has to exercise a little caution and take care of the ankle that went under the knife, but he cannot afford to let it affect his mental approach to physical competition.
“Every now and again, like just now I’m wary of it, I know I can’t push it as much as I want to in the future maybe or play through things I shouldn’t,” he said.
“As soon as I cross that white line I’m ready to go, I’m going out there knowing I’m fit.
“I’m sure if you asked every footballer if they go into every game 100 per cent I very much doubt anyone goes in without niggles.
“I can’t let it play on my mind.
“The minute I think about my ankle or pull out of a tackle then you get hurt even worse.”
The international break has presented an opportunity to further his conditioning.
Marcelo Bielsa’s United have been hard at it at Thorp Arch, preparing for another burst of Championship fixtures, starting with Birmingham City.
“It’s hard work here, really hard work. There ain’t no stopping for us.
“A lot of teams would be away, resting, which they think is right – our gaffer thinks the best thing for us is to work hard while the other boys are away playing.
“We’re playing games every day in training, big games, small sided games, trying to work on things we think will help later on in the season.
“It’s a hard week, we get a day off at the weekend to spend with our families, then we’re back next week, ready for quite a few games in a short space of time until the next one.
“We’re aiming for a fresh start when we get back.”