Plant has frequently stressed that he is not interested in touring with the remaining band members - Jimmy Page, John Paul Jones and Jason Bonham - despite reuniting with them for a one-off gig at London's O2 arena in 2007.
However, manager Peter Mensch has assured fans that the band will continue to record and tour if they can find a replacement singer.
"John Paul Jones and Jimmy Page enjoy playing with each other, Jason Bonham is a really good drummer so why not? We just need to find a singer," he told BBC 6 Music.
"[They] did the show with Robert Plant; they had a really good time rehearsing, the three of them, before Robert showed up...They decided that if they could find a singer that they thought would fit their bill... that they'd make a record and go on tour."
Mensch refused to discuss recent speculation linking Chris Cornell, Jack White and Steven Tyler to the position.
"I can't comment on any rumours right now. It's gonna be a long and difficult process. And we're not soliciting people. So don't call me about it!"