The 18-year-old praised the British boyband since their incredible run of success in the US in recent weeks.
"I already know one of the biggest artists in the world thinks Harry is so hot, but I have been sworn to secrecy," he told The Mirror.
Talking about the group's fan following in America, he added: "The single guys from One Direction are going to have a lot of fun.
"They look great, they sound great and, when you add their British accents into the mix, the American girls are going crazy for them.
"Sure you need the talent, but you need to win over the American public, that's what it is all about. One Direction are genuine good guys. The industry needs a fresh boyband, and by the end of this year they will be the biggest boyband in the world."
Justin Bieber recently congratulated One Direction and fellow boyband The Wanted on their US chart success.
The singer will release his new single 'Boyfriend' in the UK on April 8 instead of its original scheduled date of May 20.
> One Direction confirm Justin Bieber collaboration
Watch the video teaser for 'Boyfriend' below: