The pair played together in the Saints academy.
Dyer told the Daily Echo: "I'm very pleased for Adam, he's proved that he can play at that level, but I'm not surprised," said the Swansea winger, who scored against Saints on his return to St Mary's last season.
"I don't think there are many two-footed players like him in the Premiership and that's a great talent to have.
"He's literally been like that since I was in the youth team with him, and he's grown up and matured.
"Our youth team was packed with talent and [former academy coach] Georges Prost was amazing for us; he showed us how to play the right way.
"Adam's been like that all season. I'm so happy for him and that he'll get a chance for England, he's a great guy."
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