Mathieu arrived at Valencia as a fullback, before working with Valverde.
"It was Valverde who taught me how to play this position and little by little I became more comfortable," he said.
"I'm a versatile player, but I feel more comfortable as a center back, I've come here to play as a center back.
"I know that there's a lot of quality at Barça and we all have to be united in order to be successful. I like how the team plays and I hope that I can show my abilities."
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