The prolific winger made his return from a knee reconstruction by, typically, scoring a hat-trick in the friendly win against Halifax a week ago.
No one could have begrudged the 22-year-old such rewards especially as he had spent most of last season as a frustrated spectator.
But Johnstone revealed that, at particular low points, he would hold on to the knowledge that England coach Wayne Bennett was considering him for an international call-up.
Speaking to The Yorkshire Post, Super League’s 2016 Young Player of the Year recollected: “I had a phone call mentioning there was talk about me but not a specific ‘you’re in.’
“Chezzy (Wakefield coach Chris Chester) got a phone call from Kevin Sinfield (RFL rugby director) who said they were really happy with what I’d done.
“It (a squad place) wasn’t confirmed but to have people like that talk about you was a very positive thing that gave me a really big boost.
“Getting into the England squad this year is not my priority. It is good to be talked about but I’m still thinking I have a bit to do before I look at that.
“It is something that got me through my rehab, though, knowing people were talking about me.
“It made me think ‘just keep working hard, it will come, it will come.’
“I had a big aim to get back to and now I just want to kick on from where I left off before I got injured and if it’s meant to be it will happen.”
At the point where he left off, Johnstone’s stock was high; the rising star had scored eight tries in his opening dozen games before suffering that season-ending injury against Catalans Dragons last April.
The German-born player, who was brought up in Leeds, had managed 20 tries in 25 games the previous campaign and, with Super League rivals casting an envious eye, signed a new improved deal until the end of 2020.
He knows he is not necessarily guaranteed a spot in 2018, however, after Ben Jones-Bishop and Mason Caton-Brown both flourished at times on the wing as Wakefield came so close to the top-four last term.
Centre Bill Tupou also featured there on occasion and Johnstone conceded: “The side did really, really well without me which was a really pleasing thing but at the same time a really nerve-wrecking one, too, seeing the two wingers do so well.
“With our next warm-up games and the training camp we’re going on, I have to put my best efforts in to stake my claim and get that wing spot back.
“I really enjoyed getting back out there on the weekend.
“I know it was a lower league team (Halifax) we played but it was just really good in general to get out there with the lads and not have to sit and watch a game.
“Sat in the stands is the worst part of being injured. It’s an absolute nightmare; eight months of doing your rehab and just sat watching.
“That’s watching training, too. I missed training. So to get involved against Halifax was great.”
Judging by his performance in that 62-0 win against the Championship outfit, he does not seem to have lost any of his pace, power or finishing ability although, initially, he did worry about the first of those assets.
“For me there was a lot of panic just towards the back end of the rehab,” explained Johnstone, Trinity now edging ever nearer their season-opener at promoted Hull KR on Friday February 2.
“A month ago I still wasn’t getting to where I used to be on speed and I did really start panicking. People kept saying it’d be fine and it will come but I kept thinking ‘I’m playing in a month, I need to be ready, what’s going on?’ But these last few weeks, the intensity has really picked up and it all came into place all at once.
“It went really well last week. I was blowing for the first 20 minutes or so but after that it felt like I just fitted straight back in and actually felt like I’d not missed any games let alone eight months.”
Welcome news indeed for Johnstone, Trinity and perhaps, in the future, England, too.