Earlier this month, reports emerged that Walsh had ditched the boyband because of disappointing ticket sales, as well as lead singer Ronan Keating's recent infidelity scandal.
Walsh has now argued that Boyzone cannot compete with their younger, more contemporary peers.
"They're like Blue - yesterday's men," Walsh told Heat. "There's too much competition for them.
"You have to have something amazing as there's so much talent out there - JLS, One Direction, Westlife, The Wanted."
It is rumoured that issues between Walsh and Boyzone worsened following the death of group member Stephen Gately at the end of 2009.
"Boyzone can carry on but it wasn't working," he added. "It was great while it lasted, but it's time for me to move on."
The band themselves have so far insisted that they have no plans to break up.
Watch the video for Boyzone's latest single 'Love is a Hurricane' below: