Danny Coyne says he was 'delighted' to hear confirmation of George Long's inclusion in England's 21-man squad for the forthcoming FIFA U20 World Cup in Turkey.
And Coyne, who has observed the young goalkeeper at close quarters after joining the Blades last term believes Long possesses both the quality and character to prosper on the international stage.
He commented: "The biggest thing about George that stands-out for me is his attitude. He really is a rare breed in that regard.
"Everyone makes mistakes but the first time it really dawned on me that George is made of the right stuff was when I saw how he bounced back after having a little wobble early on in a game.
"That tells you he's mentally strong and he's got an amazing consistency. Not only with his performance in terms of matches but also towards his work during training in the week and in someone of his age that is very, very rare.
"I'm delighted for him and there's no doubt in my mind that he can go over there and acquit himself ever so well."
The Sheffield born stopper had been scheduled to discover whether he had made the final cut for the tournament in Turkey on Friday 7 June.
But coach Peter Taylor, whose staff includes former United defender Ugo Ehiogu, brought forward his announcement following last week's training camp in Cheshire.
Manchester United's Sam Johnstone and Connor Ripley of Middlesbrough have also been selected with Chelsea's Jamal Blackman the goalkeeper to miss-out.
"George is one of the new breed of goalkeepers," Coyne, who won 16 senior caps for Wales, said. "Big, strong, powerful and athletic.
"What really impresses me about him as well is that he never gets carried away when things have gone well. George is a really grounded lad and he always wants to know what he can do better.
"That's a great attribute and outlook to have at any age."