From being sent back to Aberdeen from a loan period at Ayr United because he was not getting a game, to skippering Scotland in the Azteca stadium aged just 21.
Everything seemed to change at a dizzying pace for the Kirriemuir-raised McKenna. There was bound to be a levelling off at some stage. That’s not to say a multi-million-pound move to Nottingham Forest is evidence of career atrophy. Far from it.
But McKenna is now seeking to make up for lost time after an injury disrupted first season at the City Ground that led to him also losing his place in the Scotland team.
Mercifully, things have not unravelled to the extent that he is no longer a member of the squad – McKenna was relieved to see his name among the 26 players Steve Clarke selected for Euro 2020, particularly when his former Aberdeen teammate, close friend and fellow centre-half Andrew Considine missed out.
Once a problem position for Scotland, this underlined just how fierce competition now is in the middle of defence. McKenna now has a couple of friendlies in which to potentially play himself into contention ahead of the finals, beginning against the Netherlands on Wednesday – three years to the day since he led Scotland out against Mexico in front of around 70,000 jubilant Mexicans waving their team off to the World Cup in Russia.
An Azteca friendly is one thing, Wembley for a competitive clash with the Auld Enemy quite another. McKenna is clear about what it would mean to him to make the starting XI in London on 18 June.
“It would probably be the best moment in my career,” he said. At present 22,000 are expected to be allowed inside Wembley for this eagerly awaited clash, although that could change.
A game that could see Scotland potentially book their place in the knockout stage against their oldest rivals is a world away from an Azteca experience when an unfamiliar Scots side had little to lose.
“It was completely different circumstances,” said McKenna. “We went with a weakened team, a younger team, whereas now there is competition for places all over the park and we have boys playing at the very top level. It’s a different squad to that one. But given the opportunity (v England), I would say that game (against Mexico) gives me good experience to lean on."
It’s a long time since a Nottingham Forest side laden with Scots became European champions for the second successive year - 41 years ago last month in fact. As the lone Scot in the Forest squad, McKenna must expect to fight his own battles when it comes to dressing-room capers. The message he arrived home to following Scotland’s Euro 2020 clinching victory over Serbia was warm – to a limit. The sting in the tail spoke of a situation where McKenna is vastly outnumbered by English teammates at the club.
“When I got back after we beat Serbia there was a big poster on my locker saying: ‘Congratulations on booking a place at the Euros and a spanking by England!’” he recalled.
Investigations remain ongoing. “I have not found out who did it yet,” he said. “It’s actually still there. I kept it there. Hopefully I can go back and I can rip it down after we beat them.”
That would register as a particularly cathartic moment for McKenna, who has endured a frustrating time of it since his £3m move to the English club.
His settling-in period was hampered by an ankle injury although he did play in ten of his side’s last 11 games of the campaign. “That was a good run for me in a bit of a stop-start season,” he said. Expected to challenge for promotion, Forest finished 16th after sacking manager Sabri Lamouchi – the man who signed McKenna – in October. He was replaced by Chris Hughton.
Such struggles at club level together with injury explains why McKenna was not completely confident about being included in the Euro 2020 squad. Grant Hanley seems to be in possession of the centre centre-back jersey while McKenna's favoured left-sided berth if Scotland employ a three-at-the back system is occupied by Kieran Tierney.
McKenna looked on from the bench against Serbia as Scotland secured their place at Euro 2020 with Declan Gallagher playing in the middle.
“Obviously, KT will be the one who plays on the left of a back three and then there will be three or four of us all battling for the other positions,” he said.
“No one was really 100 per cent certain until the squad came out, but the fact I had been given a training programme by the SFA suggested I might have a good chance," he added. "But you still have that excitement and relief at the same time when you actually see your name on that squad list when to gets announced.”
Considine was not so lucky. His former Aberdeen teammate was one of the surprise absentees and Clarke admitted that having to exclude him caused him considerable sorrow.
McKenna felt for the 34-year-old as well. He was able to commiserate with Considine in person at Cormack Park, Aberdeen’s training centre. New Pittodrie manager Stephen Glass agreed to let McKenna return to his old club to train with the defender, conscious of how much football he had missed last season, desperate to maintain his fitness levels ahead of the finals.
“He (Considine) was obviously disappointed, but he wishes the squad all the best," said McKenna. “He is definitely very grateful for the chance he had. He got three caps in the last six months. He is grateful for that, but I have no doubts he is very disappointed to miss out.”