Chelsea defender Gary Cahill says England's defence is still adjusting to the retirements of John Terry and Manchester United veteran Rio Ferdinand.
For the first time in almost 15 years, England have had to go through a qualifying campaign without the services of either Terry or Ferdinand.
"They were two huge players and they retired at similar times so there had to be a transitional period and that's what it is at the minute," Cahill said.
"We have some quality centre-backs as well, but when two big names, two big top-class centre-halves come out of the set up there is that worry. People are always going to talk about it."
