Johnstone came through the England junior teams with Butland.
"Heâ€™s done well. Heâ€™s a good lad and a good goalkeeper. Heâ€™s managed to get himself into the England squad, has been around first-team football regularly and played in the Olympics. There has been a lot of hype around him as heâ€™s been in the spotlight and heâ€™s done well to get a move to Stoke," Johnstone told manutd.com