The five-piece girl band celebrate the 20th anniversary of their debut single Wannabe this year (16) and had been discussing potentially teaming up once again to mark the occasion.
Following claims that Posh Spice Victoria Beckham had refused to take part in the reunion due to her fashion career taking priority, now Britain's The Sun newspaper has reported that Chisholm, aka Mel 'Sporty Spice' C, has thrown a spanner in the plans.
"Mel C is out of the reunion for now," a source told the publication. "She has essentially left the band to focus on a more serious music career. She loves the girls but it just didn’t feel right for her to reunite with them at the moment. She has other priorities and obviously it was a bit of a problem that Victoria made it clear she wasn’t going to be part of the reunion."
"At the end of the day, Geri left the group in 1998 and they were able to continue with the four of them, which is why they could accept Victoria’s decision, but losing Mel C might be a bridge too far.”
Despite Chisholm's decision coming as a disappointment to bandmates Ginger Spice Geri Horner, Scary Spice Melanie Brown and Baby Spice Emma Bunton, the trio are said to still be determined to mark the anniversary in some way. They are apparently discussing either touring as a three-piece or enlisting the help of some other singers.
"Mel B and Geri in particular are still determined to mark their anniversary in some way," the source added. "They are arranging a number of meetings which include the option for a tour, possibly with just the three of them or with other singers."
In fact, there have even been talks of a Spice Girls talent show, the source added. The programme would give the public the chance to audition for a place in the band - in a similar format to The X Factor.
"It would be an absolute TV sensation," the source said. "Could you imagine the opportunity for a member of the public to become a Spice Girl?"