Despite heading into the tournament off the back of nine consecutive victories without conceding, Stuart Pearce's side were comprehensively beaten by both Italy and Norway in their opening two group games.
And Campbell, who represented the Under-21 side while a first-team regular at Tottenham between 1994 and 1996, feels players can get ahead of themselves in terms of ability, allowing complacency to creep in.
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"There are some really good players coming up but on the whole a lot of them think they're there already. There's a lot of other countries around the world with very good players at the top of their game but they continue to work hard, not believing they've made it yet.
"They may be playing for their first team already but they don't lose it. You keep on learning. You've got to keep on striving. That's the way I feel English football has gone."
The Premier League recently boasted record television revenue for the last financial year, with £2.4 billion, and while Campbell welcomes the success and ability to attract star players from around the world, he feels it is evident such imports are restricting younger England-born talent.
"Money attracts these quality players from around the world," Campbell continued. "Italy had a lot of money back in the 80s and they attracted all the good players, then they had to change and say they would have three foreigners and that's it. Now it's Spain and a fantastic programme going there.
"In England it's too much money but it's how you use it, how the young players get through the ranks. If there's too many foreign players and they're top players I'm all for it but if [youngsters] can't get through, something's got to happen."