Kym, 25, who is dating EastEnders star Jack Ryder, is also said to be upset at plans for Hear'Say to perform for British soldiers in the Middle East.
'Wants to be a solo star'
But a spokesman for Hear'Say's record company, Polydor, told us that Kym had not walked out on the band.
He admitted Hear'Say would be holding talks to discuss their future.
Reports claim that Kym wants to write her own songs and become a solo star.
Other reports say Myleene, Suzanne, Danny and Noel are being urged to carry on without Kym.
Even people close to the band don't seem to know what's going on.
On Sunday, CBBC Newsround Online spoke to a band insider - who told us he had "no idea" if Kym had left the band or not.