The 19-year-old goalkeeper, who has just completed a breakthrough season in the first team at Bramall Lane, hopes to be involved in Sunday's opening group fixture against Iraq.
"It's always the biggest honour you can have to compete for your country," Long told the club's official website.
"I feel proud to be involved, very proud in fact and now I just want to try and do well."
Long, who made 44 appearances for the Blades last season and voted the club's young player of the year, added: "We want to do well and hopefully give the nation a lift after the Under-21s failed in Israel.
"I'm really enjoying myself here and we all get along great. When you go into a tournament it's important to have a good team ethic and group spirit. We've definitely got that here."
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