But the 20-year-old forward - the subject of several prank calls from team-mates - revealed his delight after being named as the only uncapped player in head coach Frank Hadden's 30-man pool heading to France next month.
John's omission from Saturday's 22 set the alarm bells ringing but thankfully for the former Dollar Academy pupil it was just Hadden's way of testing his nerve.
John said: "When I was left out of the Ireland 22 I was very disappointed and I thought that might have been my last chance.
"So it was a lovely surprise to come in on Monday and find I had not been left out."
Hadden's decision to go with 17 forwards and 13 backs favoured John's inclusion, however he admitted having no inkling as to the national coach's thoughts right up until the squad were inside the tunnel at Murrayfield.
He added: "We were told that if we were not in the squad we would get a phone call from Frank on Monday morning so there were a few people texting and phoning trying to give me a fright!
"The worse time was waiting for the call and not having that confirmation.
"I was thinking that maybe Frank had phoned me when I was on the phone to someone else and left a message I hadn't got.
"I had all sorts of things going through my head.
"Inside I knew Jason White, Simon Taylor, Kelly Brown, Allister Hogg and Dave Callam were going, having played most of the Six Nations matches.
"I thought it was going to be between me and Alasdair Strokosch, if indeed any of us, or just if someone got injured."
Strokosch missed out but John has clearly impressed Hadden with the levels of consistency and approach to training.
The player himself feels his contribution at Glasgow towards the end of the season could have been the catalyst to his inclusion.
And he is desperately hoping to get his chance in the final warm-up match against South Africa on August 25, before the Scots face Portugal in Saint-Etienne on Sunday September 9.
He added: "I had quite a slow start to the season and results maybe didn't help but then Glasgow as a team picked it up and had a very good few last months to the season.
"That helped me play better and I got to the Churchill Cup and that was perhaps the springboard to this.
"It is strange to be the only uncapped player and I am hoping, although there is no guarantee to get the chance either next Saturday or at some point in the World Cup to show what I can do."