"If you're Ronan Keating, who was working in a shoe shop when I discovered him, but end up thinking you're George Michael, then you need to be stopped."
Walsh (60) said he was fed up with Keating (35) and other pop acts getting ahead of their station and believes that pop singers shouldn't try and write their own songs. "That rule is for people who have no talent, like Ronan Keating," he said.
Walsh went on to say that the Australian X Factor judge has an inflated opinion of himself, and now "seems to think he is the new George Michael".
Louis, who formed Boyzone in 1993, says Keating needs to be cut down to size.
Boyzone were one of Ireland's most successful boyband and have had 21 singles in the Irish top 40 charts.
Now Louis says fame has gone to Ronan's head and that the singer now believes his own hype.
He also criticised Ronan's ability to write his own songs.
"His head got turned by having nice hotels and chauffeur-driven cars and he thought he could write songs," Louis told Q Magazine.
"I get very annoyed by talentless, spoiled pop stars. They need old-school management. But obviously Adele is a different case. I'll never work with an artist who won't do as they are told."
Walsh and Keating always had an intense and tumultuous relationship. During Boyzone's heyday, Ronan was the golden boy of the group and cited Walsh as his role model. But things started to sour when the boys temporarily spilt in 2000, reforming in 2007.
Last year, Louis dumped Boyzone halfway through their Brothers tour, telling the press and Keating that they should split for good.
Ronan, meanwhile, has described Louis Walsh as "simply not a nice character".
Ronan is currently a popular judge on Australian X Factor and splits his time between Dublin and Sydney.