The goalkeeper has been in outstanding form for the Baggies throughout the 2020/21 campaign.
And those impressive performances were rewarded last Thursday when he was named in the senior England squad for the very first time.
With current number one Jordan Pickford injured, Johnstone was called up alongside fellow goalkeepers Nick Pope and Dean Henderson for the upcoming World Cup qualifiers against Sam Marino, Albania and Poland.
But as a new face in the squad, the Baggies goalkeeper knows the pressure is on to really impress manager Gareth Southgate and his coaching staff.
“I have trained twice and it was great,” Johnstone said. “As soon as I walked through the doors, I just wanted to get out on the pitch and get going.
“It’s something special to be here.
“It’s the dream isn’t it? To be called into the senior squad. I’m delighted to be here, I’m really proud and I’m enjoying it.
“I’m enjoying the challenge of being here and being under pressure.
“I’m with top players here and everybody is watching the new faces in the camp. I want to make a good impression.”
With Pope expected to start England’s three games, Johnstone was asked how he would feel if he was told to come off the bench for his senior international debut.
“I’d be buzzing,” the 27-year-old added. “The adrenaline would be going.
“That is what you play every week for – to be in the national team and hopefully play for your country.
“Jordan Pickford is the number one but everyone else is here to push each other.”