Gareth Southgate has been forced into a defensive rethink after John Stones was ruled out of England Under-21s' first two European Championship matches with suspected concussion.
One of the Young Lions' key men, the Everton defender was set to start Thursday's Group B opener against Portugal in Uherske Hradiste.
However, fears were raised over Stones' availability when the defender failed to emerge for training on the eve of the match, with what was described as a head injury.
Under-21s head coach Southgate has now confirmed he has sustained suspected concussion, ruling him out of the opener against Portugal and Sunday's clash with Sweden.
"We've just one concern over John Stones, who picked up a head injury so unfortunately it looks like he will miss the game with suspected concussion," Southgate said.
"It is a great shame for him first and foremost. He has been looking forward to this immensely and he is bitterly disappointed.
"Our first thoughts are to lift his spirits as quickly as possible. In terms of the group, we have a strong mentality.
"In all positions, we've had players that have moved up to the seniors, so we've had to look at others players during the campaign.
"We've got great competition for places in every area of the field and throughout the competition we've not just relied on picking a first 11.
"I've tried to make changes each time for this sort of reason - you know when you get to the finals anything can happen.
"We're ready to deal with that, the group is very strong and it's obviously a great opportunity for somebody else."
Middlesbrough's Ben Gibson looks likely to be the beneficiary of Stones' unfortunate setback, sustained on Tuesday during a closed training session.
As per Football Association guidelines, he cannot return for at least six days after the incident and Southgate wholeheartedly backs such caution.
"We have no option at all on it," he said, speaking at the Mestsky Fotbalovy Stadion. "It's a very clear guideline and rightly so.
"The priority is our player's welfare - football isn't as big as that.
"We think he would have to miss (Sweden) as well. Hopefully the recovery period is very clear provided he continues to hit the markers as he goes through."
Southgate has no intention of sending Stones back to Everton - "We would struggle to pack him up anywhere at the moment," he said - and expects him to be available for final Group B match against Italy.
The injury is hardly the ideal preparation to face a Portugal side awash with talent and who reached the Czech Republic with the only perfect record in qualification.
England did overcome them 3-1 seven months ago in a friendly at Turf Moor, but their opponents can now call upon eight senior internationals.
"I think that we know that we've got really good options," Southgate said. "We feel that this is a high-quality game.
"We know that Portugal have got a very good side, we played them already in November.
"They've got players to come back from that, so have we and we recognise it is a great challenge for us."
Source: PA
