The actor invited her to join him on his UN mission to Darfur and revealed that she was his favourite member of the group.
During an appearance on US TV show Good Morning America, her bandmates urged him to dump girlfriend Sarah Larsen and hook up with Halliwell.
Mel B said, "She is single, take her out", while Victoria Beckham added: "He should invite her out for dinner. Definitely."
Halliwell admitted that she was delighted with the praise, saying: "It's very flattering knowing I'm George Clooney's favourite Spice Girl."
However, recent reports claim that Larsen, 29, is on the verge of moving in with Clooney at his Hollywood home.