The 26-year-old Glasgow Warriors lock forward is among 17 uncapped players named in the 37-man squad for Scotland’s summer tour.
And the former Killermont Primary and Boclair Academy pupil admitted: “It was completely out of the blue.
"I got a call the day before it was announced from the forwards coach John Dalziel. He just explained they'd been keeping a close eye on me and wanted to include me in the squad and see how it goes.
"I'm absolutely over the moon. I didn't expect it at all and I still can't believe that I've been included.
"It's the highest you can go internationally to represent your country. Scotland is my home, I'm a proud Scotsman and I can't wait to get the chance to hopefully represent the nation."
The Scots will play a match against England A down south on June 27, followed by back-to-back tests in Romania and Georgia on July 10 and 17.
And while summer squads are traditionally weaker due to injury, unavailability and – as is the case this year, British Lions commitments – McDonald is also aware that creates an opportunity for others to impress and stake a claim for full-strength squads later in the year.
"Absolutely,” he said. “You've just got to take every opportunity you can because you might just get that one opportunity and it will be make or break for you.
"I think the whole idea of this summer tour and the squad which has been announced is to give the opportunity to see how guys go and that will definitely give the coaches an idea of where guys are at.
"There's a lot of injuries but without those injuries anyway I think it would have been a similar squad."
Yet Kiran revealed that rugby wasn’t a path he was guaranteed to follow when he was younger.
He said: “I went to one West [of Scotland] training night but was kind of juggling loads of different things at school, playing football and athletics, so I didn't have much time for rugby as a kid.
"But I joined Glasgow Hawks as one one-off to see how it goes when I had a bit more time and it's gone from there really.”