The Aberdeen defender won his first cap in Scotland’s 1-0 friendly defeat to Costa Rica at Hampden and grew in stature as the game progressed.
This time last year the 21-year-old was out of favour at Ayr during an unhappy loan spell which culminated in relegation.
But an appearance for Scotland Under-21s in a victory over Holland in September propelled him into the thoughts of Dons boss Derek McInnes, who handed him a start in a 1-0 win at Motherwell weeks later - and McKenna has never looked back.
When asked how he reflected on his progress, the centre-back said: “I have not really thought about it but if you had told me at the start of the season I would have a cap for Scotland, I would never have believed you.
“I wasn’t playing for Aberdeen, wasn’t involved for the 21s. It just all seemed to happen so quickly.”
The first cap also caught McKenna by surprise when Alex McLeish named the first starting line-up of his second spell as Scotland manager.
“It was definitely a surprise,” he said. “Just to be involved in the squad was a surprise itself. When the team got named this afternoon, to see my name on the board I was delighted. I wasn’t expecting it at all.
“I have only played 20-odd games for Aberdeen this season. There are boys out there who have done it consistently over a lot more games. I was thrilled to get a chance and I just wanted to go out and show what I could do.
“I was a bit nervous at the start but once I settled into the game, with obviously the experience of Charlie (Mulgrew) beside me and Andy Robertson, who is playing at a very high level, I thought I slotted in comfortably enough.”
McLeish had some simple words of encouragement for McKenna.
“He just said to me to go out and do what I had been doing for Aberdeen, that was the reason I was picked,” the defender said.
“I just tried to keep it simple, defend well, and give it to the boys who are more influential on the ball and let them do their stuff.”
McKenna’s delight at his first cap was tempered by the result but there were some encouraging signs after Marco Urena’s 14th-minute opener.
“I thought we started a bit slow, maybe just a lot of new boys on the pitch at the same time and didn’t really know what to expect,” said the defender, who was one of five new caps.
“But (in the) second half I thought we were a lot better and pressed up the pitch a bit more and created a couple more chances, which we maybe should have scored from.”