Viva Forever!, which features the British girl group's music, was written by Absolutely Fabulous star Saunders and produced by Judy Craymer, the brains behind hit show Mamma Mia!
However, it opened in London's West End last month to a slew of scathing reviews, with critics labelling the production "insultingly banal", "tawdry, lazy and unedifying" and a "clunker".
Subsequent reports suggested producers were considering shutting the production down as venue bosses are struggling to fill seats at the Piccadilly Theatre, but Saunders is adamant reports of an early closure are not true.
In a post on her Twitter.com page, the funnywoman wrote: "Get [got] show report but having withdrawal from Viva... Despite Daily Male [Mail, British newspaper] predictions show goin v (very) well thankee (sic)."
A spokeswoman for Craymer went on to blame the disappointing box office figures on the annual post-Christmas slump which affects the whole of London's famed theatre district: "The West End takes a dip at this time of year. But the show is doing really well."
Spice Girls stars Melanie Chisholm, Emma Bunton, Melanie Brown, Geri Halliwell and Victoria Beckham have all backed the big-budget stage show and they reunited in London for the production's opening night last month.