Despite his heroics against Celtic, Johnstone found regular first-team outings in the number '9' jersey hard to come by, largely due to the presence of Colin Stein, Scotland's first £100,000 player, although he did score 11 goals in 16 league appearances during the 1971–72 season. He compensated for his lack of frontline action by often playing as a centre-back when either Ronnie McKinnon or Colin Jackson was injured, and when the duo were ruled out of the 1972 European Cup Winners' Cup Final, Johnstone (still only 18) deputised in the match against Dynamo Moscow.