Coyle recently rejected the suggestion from Kimberly Walsh that her relocation to Los Angeles was holding up the girl group's comeback.
However, a source told Heat: "The other four are in regular contact and see each other when they're not working. Nadine holds them back.
"She's so far removed from the band it's like she's left already. Nadine's jealous. Once upon a time, Nadine was the 'lead singer', the one the tabloids wrote about. Now everyone's forgotten about her."
It was also reported that Coyle did not get in touch with Cheryl Cole when the X Factor judge travelled to Los Angeles following her split from husband Ashley.
> Nadine Coyle 'perfecting' solo album