Johnny McDaid, who has been writing songs with Styles' for years, said the British musician's solo songs will "blow the socks off the world," reported Aceshowbiz.
"I've been friends with Harry for a long time, and we've written together a lot. Harry is a really prolific artist and a super-talented guy. He's really authentic and he has an incredible voice, so we've been writing a lot of songs. We've been writing songs for years together.
"I'm really excited by the way he's sounding at the minute, he's such a talent. I think the world is going to be really shocked at what he comes up with... It'll blow the socks off the world," the Snow Patrol member said.
The singer, who will be making his acting debut with Christopher Nolan's upcoming World War II movie, recently cut his signature long hair for a role.