Walsh started the feud earlier this week when he branded Contostavlos a "chav in a tracksuit".
Contostavlos hit back at the Irish music mogul, mocking his lack of recent chart success.
Talking on the red carpet at yesterday's X Factor series nine launch, Walsh said: "I've sold millions of records, I've had 30 number ones - when did she last have a hit?
"I'm not old, I'm just experienced. She's young, she's got no experience.
"What does she know? She's had one hit! I just tell it like it is."
When asked about his comments, Contostavlos accused the X Factor veteran of deliberately trying to "wind [her] up".
"He knows what he's doing," she said.
The X Factor launches on Saturday, August 18 at 8pm on ITV1.
Photo gallery - X Factor launch 2012: