England manager Roy Hodgson fears "inexperience or a lack of quality" may be his side's undoing at Euro 2016.
Hodgson's team qualified for the finals in France with a 100% record and beat the hosts 2-0 at Wembley on Tuesday.
That side contained six players aged under 23 and Hodgson wonders if their youth will be an issue.
"You don't turn a guy who has played six or seven Premier League games and once for England into a Frank Lampard or Steven Gerrard," he said.
"I do believe we will have the organisation, the discipline and the desire.
"If we fail it might just be because some of the teams that beat us have got that player or two who can turn a game."
Hodgson has been in charge of England since May 2012 and his team have only lost once in 16 matches since coming bottom of their group at the 2014 World Cup in Brazil.
He is pleased with the side's improvement, but says the young players are still learning at international level.
"I believe in the players and, given the opportunities, can become a good team but we are young, we are inexperienced - nothing is going to change that," added Hodgson.
"When Paul Pogba came on for France there was a definite acceleration in the quality they showed - we have got to get players up to that level of quality.
"It's still six or seven months away and I'm optimistic, positive and hopeful. This group of players won't let anyone down in terms of their attitude and desire.
"If they do fail it might just be because of inexperience or a lack of quality."