The Eagles will vie with seven-time UEFA Europa League winners, and reigning champions, Sevilla at Detroit’s Comerica Park on Sunday night (kick-off 19:00 EDT local time/Mon 00:00 BST local time), capping the second leg of their US pre-season tour.
And with the new Premier League season now just two weeks away, Johnstone believes facing a team of Sevilla’s calibre is a unique, but exciting, acid test of Palace’s preparations.
“It’s a big test for us,” Johnstone said. “They’re a great team and it’s not often you get to play a team like that, and one from La Liga.
“It’ll be a great game, and the lads are looking forward to it. Hopefully there’s a big crowd to come and watch it, because I think it’ll be a good game.
“We play in the Premier League, and they play in La Liga – two massive leagues. For people to come and watch would not only be great for them, but also great for us to have that support.”