Amelle Berrabah has been hospitalised with nervous exhaustion.
The Sugababes singer will take a three-week break from the band to stay at a private health facility after recent stresses within the band - which saw original member Keisha Buchanan replaced by Jade Ewen - became unmanageable.
A statement from her bandmates Jade and Heidi Range read: "Unfortunately, Amelle has been forced to take an unexpected short break away from the pressures of work, following some professional medical advice earlier this week. It seems that with all the recent events in the band right up to Jade joining us a few weeks ago, the stress over a period of months has unfortunately taken its toll on Amelle and she is now suffering from a severe bout of nervous exhaustion.
"For the next three weeks, Amelle will be staying at a private health clinic in Europe where she will be able to rest and recuperate under expert supervision. We're expecting her to return to work in full health by the beginning of November."
Heidi also spoke about the "traumatic" time she and Amelle have had in recent week and thanked fans for their support.
She said: "Both Amelle and I have been through a very traumatic time together in recent months and particularly over the past few weeks. Having the opportunity to move forward with Jade was a major factor in us both deciding to carry on as Sugababes.
"And judging from the thousands of well wishes we have received from you, our fans, we are delighted that we made the right decision. However, the months leading up to that decision certainly took their toll, especially on Amelle, and it seems like it's now all caught up with her."
Promotional duties will still be carried out by Heidi and Jade in Amelle's absence, but planned performances, including the new line-up's debut in Leeds on Sunday (18.10.09), have been shelved.