Former England captain Terry Butcher admits he is worried England's defence lacks "resilience" ahead of Euro 2016.
However, the former England centre-back and captain believes Roy Hodgson's men have enough quality in attack to reach the semi-finals.
The 57-year-old, who made 77 England appearances, has reservations about a defence in which Chris Smalling, Gary Cahill and John Stones are the only recognised centre-backs for Euro 2016.
"It's an exciting squad, one of the youngest squads England has ever produced," Butcher said.
"It's based on attack, going forward, scoring and creating goals. The best form of defence is attack. At the back, it still worries me.
"We give away some silly and easy goals. There doesn't seem to be a real resilience, a real steely determination not to concede.
"It seems to be just a case of hoping that teams don't score, rather than saying they definitely won't.
"That will come. We found that in tournaments that you got more understanding, more determination, more spirit when you're together all the time."
Butcher, speaking ahead of taking part in his second Prostate Cancer UK Football to Amsterdam cycle challenge, says that work on the training ground will be critical.
"The thing about England in training is that the defenders are up against very good attack-minded players in the squad," he said.
"We always found training sessions extremely hard, because you're up against really class players. That's the same now with England.
"England's defence - if they can keep out England's attack and midfield players - then they won't face many more difficult opponents in the tournament itself."
Despite England struggling to overcome 10-man Portugal 1-0 at Wembley in their final friendly before Euro 2016, Butcher believes Hodgson's side can do well in the competition.
"I'm optimistic. I think they can go through to the last four," he said.
"Spain are the holders and Germany the World Cup winners, but England have played those two teams and know what they're up against.
"There shouldn't be any real worries for England about the opposition. It's a case of what England do themselves, more importantly."