Speaking to Absolute Radio's Ben Jones, Plant said:
"The reason that it stopped was because we were incomplete, and we've been incomplete now for 28 years. And no matter what you do, you have to really guard the discretion of what you've done in the past and make sure that you have all the reasons in the right place to be able to do something with absolute, total conviction."
He continued: "To visit old ground, it's a very incredibly delicate thing to do, and the disappointment that could be there once you commit to that and the comparisons to something that was basically fired by youth and a different kind of exuberance to now… it's very hard to go back and meet that head on and do it justice."
Until recently, Page and Jones - plus Jason Bonham, son of original drummer John Bonham - were planning to find a new vocalist. But in January, Page's manager Peter Mensch told MusicRadar that Led Zeppelin is now "over".
More work with Alison Krauss
Plant declined to say much about his second forthcoming album with bluegrass singer Alison Krauss, but joked: "Last night's title for the next project was called A Gated Community, because it's like being in a looney bin."
Plant and Krauss's first duet project, Raising Sand, is nominated for five Grammys at the awards ceremony on 8 February.