Gareth Southgate has warned that Harry Maguire's lack of playing time for Manchester United makes it difficult to guarantee he will start games for England.
Maguire, who became the world's most expensive defender when United signed him for £80 million ($100.97m), is no longer a first-choice centre back for his club despite being named the team's captain.
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He has fallen down the pecking order behind Lisandro Martinez, Raphael Varane and Victor Lindelof, with even left back Luke Shaw having played in central defence, leaving Maguire with just seven starts in the league this season.
"Inevitably it's not a situation that can continue forever," said Southgate, who has handed Maguire over 50 England caps and included him in the squad for next month's Euro 2024 qualifiers.
"It's like Kalvin Phillips. They are important players for us and with Kalvin we haven't got many players who can play as that single pivot.
"Of course the longer that situation goes on the more concerning it is and we've got, in Marc Guehi, Lewis Dunk, Tyrone Mings, players who are playing well without the same experiences of club European football or international football.
"But we've got to keep searching for competition in that area of the pitch."
England named their squad for the next month's Euro 2024 qualifiers against Malta and North Macedonia and left out Raheem Sterling, who has been a key player for Southgate since he took charge of the national team
Sterling has struggled to find consistency in his first season at Chelsea and Southgate said the club's constant changes have affected the player.
"I found him positive, strong, understanding what's gone on," Southgate added. "Difficult for everybody with all the changes this year at the club. Three different managers, three different ways of training, three different ways of playing, so a lot of upheaval. Clubs have these moments.
"If I was looking at him I would always back him to respond strongly and to have the resilience and tenacity to prove himself. He said himself earlier in the week he has not been happy with how it has been. That would be a temporary thing for sure."
Information from Reuters was included in this report.