The veteran TV icon responded to recent comments made by Walsh during his warm-up at the launch of Strictly Come Dancing's latest series.
Walsh recently stated that the legendary Strictly presenter should have already retired from showbiz, while he previously claimed that Forsyth "shouldn't even be alive" and that he should "bow out gracefully".
Forsyth said to the audience: "I want to say I never called Louis Walsh a jumped-up karaoke judge. That was someone who wrote into a magazine who said that. They said it because Louis Walsh said that he thought I should be dead! But he apologised for that so that was fine.
"But then he's done another interview this year and started it all again, saying I should retire. He's said that next year will be his last X Factor and he'll know when to retire."
He added: "Poor Louis. What will he do when he leaves the show? Well, he can always make a comeback I guess... Except he's never been anywhere in the first place."
Strictly Come Dancing debuts on Saturday, September 15 at 6.30pm on BBC One.
Kimberley Walsh has revealed that her Girls Aloud bandmates urged her to take part in the show.
Photo gallery - Strictly Come Dancing launch: