The group were eliminated from the competition in last night's show after finding themselves in the bottom two for a second consecutive week.
Offering advice to the girls on The Xtra Factor, Walsh revealed: "I think they should stick together. I think they should find a fifth member and take their time - because they could be a great, great girlband."
He added: "They've learnt an awful lot, this business is tough - I've had lots of knocks my whole life. I have to say, they sung their hearts out tonight - they were incredible."
Meanwhile, band member Layla Manoochehri insisted that she wasn't disappointed to be axed at such an early stage.
She said: "We always said that we wanted to get to the live shows and anything plus the live shows was a bonus, so we lasted one week more than we thought we would."
The X Factor continues next Saturday at 7.45pm on ITV1.