Barnes feels Johnson is the man for England's future.
"Adam will be an automatic choice for England one day, I feel," Barnes, who won 22 caps for his country, told the Manchester Evening News. "I feel Fabio made a mistake in not taking the lad, but I also feel he should have put Joe Cole on against the Americans.
"He is not a winger, but he has played well for England on that left-hand side - and he is more technical than the rest of the England wide men.
"Shaun came on and perhaps was trying too hard, and things can go wrong when that happens.
"But I would have taken Adam to South Africa. A young lad like that has no worries - I played for England at 20.
"If he starts next season well, he should walk into that England team."