The group has earned USD 1 billion this year from their albums and tours, but Greg insists that money is not a big deal for Niall, reported Contactmusic.
"I think he will cope well whatever happens. Niall doesn't spend that much money or talk about money, it's not a big thing in his life," he said.
"Obviously it's amazing if the band go on to make a billion in a year, and I, for one, hope they do, but it will not change Niall. I know that much," he added.
It is speculated that the band will earn USD 270 million from their forthcoming 'Where We Are' stadium tour to be held in 2014.