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."
Lee, 28, wants to defend his world title a minimum of three times in 2016.
His next contest is a mandatory defence against American Eric Hunter, 29, and, while purses are negotiated, Lee is hopeful of home comforts after beating Mexican Fernando Montiel in Arizona in October.
"Ideally I'd like home advantage for that fight, because with the mandatory defences it can be really tough and any advantage you can get is welcome," he said.
"But at the same time, I don't really mind if I travel to America for the fight.
"After the mandatory, we look for a big fight in the summer and then go back to America in the autumn and try for a unification fight. That's the plan for 2016.
"I want to build my name in America and become a worldwide star."
Watch the full interview on the BBC Sport Wales programme on BBC Two Wales on Friday 15 January from 20:00 GMT
Welshman Andrew Selby can eclipse Joe Calzaghe and become Wales' greatest ever boxer, says his brother Lee.