Younger sibling Andrew, 27, has won his first three professional fights and his next bout is in Newport on 6 February.
“If Andrew trains and lives the life of a professional boxer, he could be the best Welsh boxer ever,” his brother Lee told BBC Sport Wales.
IBF world featherweight champion Lee Selby also warned his brother against complacency.
Lee, whose IBF world featherweight title defence against Eric Hunter is currently being negotiated, has won 22 of 23 fights.
He added: “I believe my younger brother is going to be the next world champion to come out of Wales.
“In all the time I’ve been boxing, since I was eight years old, Andrew has the most talent of anyone I’ve seen.
“Talent only gets you so far though; you need the determination and will to win.”