Walker is a certain starter on Sunday for the game against Croatia even though he says the players have not been told yet.
But he did suggest the prospect of Luke Shaw playing on the left side of a back three is unlikely.
Walker told Talksport: “I don't think I can remember Luke being in a back-three in training so that might have been when I wasn't here.
“But we have personnel who can play in different positions and that is good."
And Walker revealed how set-plays were featuring heavily in the most recent training sessions.
He said: “We all know our responsibilities on set-plays because we proved in the last World Cup that they are massive in big tournaments.
“Getting a few set-play goals and defending them very well can put you in good stead to last in the tournament."
Walker hopes they can last even longer than they did at Russia 2018.
He added: “We are confident. England don't normally start tournaments too well but England don't normally get to a semi-final, which we did.
“Hopefully we can keep knocking down the barriers that are around us and the cliches that are around England.
“Let's not get down, keep going and keep fighting until we can't go any further."
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