Despite playing hairdresser Candice Stowe for six years, the actress apparently felt that the soap's scriptwriters favoured her fellow cast-members Tina O'Brien (Sarah Platt) and Samia Ghadie (Maria Sutherland).
The newspaper claims that Sanderson told former boyfriend Jamie Meakin about her frustrations.
"The whole thing about Nikki leaving Corrie for love and a singing career is really only half the truth and bit of a smoke screen," Meakin revealed.
"Basically she hated the way she was generally treated. We had long chats about how she felt Tina and Samia were always given the better storylines and recognition.
"She would say, 'I'm just as good as anyone else' and get all upset. To be honest, Nikki was jealous of the attention Tina and Samia got all the time."
Nikki has denied the rumours, explaining, "I've never felt sidelined by anyone.
"You only have to watch the show to see that I've had some fantastic storylines which I have thoroughly enjoyed. The only person who knows the real reasons why I'm leaving the show is me.
"I knew there would be speculation but to say things that aren't true hurts."