The Girls Aloud singer is thought to be seeking treatment at an undisclosed location abroad.
"Sarah Harding has entered a treatment centre for depression and alcohol addiction," a spokesperson for the band told The Sun.
The paper quotes a friend of the star as saying: "She's been through a traumatic time in her personal life and had to honour her work commitments on top. She needs some time out to clear her head."
The insider also claimed that the end of Harding's relationship with Tom Crane had affected her, adding: "It all just got the better of her. She had been with Tom for a long time. All her plans for the future suddenly came crashing down.
"She was burying her head in the sand, but now she is getting support."
Harding recently made her catwalk debut at London Fashion Week and will appear alongside Judi Dench, Danny Dyer and Cliff Richard in a big-screen adaptation of play Run for Your Wife when it is released in UK cinemas next year.
She is believed to have called off her engagement to her DJ fiancé Crane last month, although it was reported last week that the pair were planning to meet and discuss their relationship.