The Irish singer was asked about the boyband in a recent interview with Britain's Real Radio Yorkshire and MCFadden singled out Horan when the host urged him to pick which singer he thought would be the first to launch a solo career.
MCFadden now reveals the comment sparked a backlash from the group's fans and he received a slew of threatening messages via Twitter.com.
He says, "I wouldn't wanna (sic) f**k with their fans. I was asked who I thought would be the first to leave One Direction on the radio - I didn't know (who to choose), but they (the hosts) said to pick one, so I said Niall because I'm Irish, he's Irish, and he has that glint in his eye. Then I get these Twitter comments from nut jobs (sic) like, 'Go f**king kill yourself'. I'm like, 'Calm down.' They're f**king nuts... It's different now because of Twitter - you can see how crazy people are."