Stuart Pearce has warned England might never end their 45-year major trophy drought unless players and clubs started taking the European Under-21 Championship seriously.
Pearce's plan to field the strongest possible side at this month's tournament has been repeatedly undermined by the withdrawal of key players during the past three weeks.
Four of the six senior internationals head coach Pearce named in his 40-man provisional squad have now pulled out, with Kieran Gibbs joining Jack Wilshere, Andy Carroll and Micah Richards in crying off and Pearce said: "I've got a breakdown of all the nations here, how many of their players that have represented the seniors, and we've probably got maybe the biggest number of absentees."
He added: "We need to make sure that when we turn up to these tournaments that the big, big players are here.
"We've got a lot of lessons to learn and the one reason I would say that is you look at the trophy cabinet - it never lies. Look at the Spanish trophy cabinet - it never lies."
Wilshere's withdrawal was the most controversial, the Arsenal midfielder reneging on his promise to play after being convinced by his manager he would suffer burnout.
Pearce said: "Draw a comparison between some of the Spanish players and see what they've done.
"Have a look what Bojan's done. This is his second under-21 tournament. For me, football's about playing football and that's what you should do."
He added: "I don't see a downside if I'm honest with you in coming to play for your country - I never have done. They're playing against the best players that Europe has got to offer, in a three, four, five-game scenario that we've got here. There's so many upsides to it. It adds value to the players, which obviously the club pick up on as well.
"I'll still deem that there's a real learning curve from the tournament like this. It's really high-profile, it's gaining in momentum profile-wise every two years. And it's a mouthwatering prospect for our players to take on the best Spain have got to offer on Sunday."