And apparently the singer is having difficult settling in, and has even said she wants to quit rehab for good.

An insider told the magazine that doctors are worried: "They’re in shock at what bad shape she’s in."

They added that having to enter rehab seems to have really upset the singer.

"She’s angry at her family and her manager for pressuring her to enter the program. She feels she was ambushed."

Britney’s representatives were unavailable for comment.

Britney suicide watch claims ’untrue’ - Feb 26 2007
Britney Spears’ manager has denied reports claiming that the troubled pop princess is on suicide watch.

Larry Rudolph said the stories were "absolutely untrue".

The singer went into rehab for the third time in a week on Wednesday night, after prompting concern about her health with her erratic behaviour - which included shaving off her hair.

Estranged husband Kevin Federline has apparently visited her at the luxurious Promises facility in Malibu.

Speaking to entertainment news show Extra, Mr Rudolph said of the suicide watch claims: "The story is absolutely untrue.

"She is in rehab, and it is very disappointing that various media outlets are running these false stories about her, as Britney tries to get better."

K-Fed, 28, and Britney, 25, are involved in a custody battle over their two young sons, but People reported that the wannabe rapper had been to see her as she started a treatment programme.

"He cares a lot about her," a source told the magazine.

Last week Britney’s father, Jamie, said his daughter was a "sick little girl".

"We’re just trying to take care of her," he told Fox News.

Rehab ’could help’ Brit keep custody - Feb 23 2007
Britney Spears’ decision to check into rehab could help her in the custody dispute over her two young children, according to lawyers.

When the pop princess checked into Promises in Malibu yesterday, it was said to be the third time in a week she has checked into a rehab centre.

Britney and her estranged husband Kevin Federline are fighting for custody of their two sons.

"It actually may reflect well on her that she’s now gone back, if she stays and sees herself through the programme," said Jason Adess, a family law attorney in Chicago.

"That way she can present to the court that she has an issue, she has acknowledged the issue, she has gotten help and now she is able to resume primary custody of the children."

Brit’s manager, Larry Rudolph, confirmed in an email to the Associated Press yesterday that the star was in the Malibu centre.

The 25-year-old pop star reportedly first checked into Promises on Tuesday, then left on Wednesday morning.

Late last week she reportedly checked into a rehab centre in the Caribbean, only to leave the next day.

Britney ’checked out against centre advice’ - Feb 22 2007
Britney checked out of rehab against the centre’s advice, according to a magazine.

The shaven-head singer left the Promises residential treatment centre in Malibu, California, according to showbiz website TMZ.com and TV shows Entertainment Tonight and Extra.

But a source has now told People magazine: "If she comes back for treatment, Promises will have to assess the situation, they said.

"Sometimes people come back, but it doesn’t look good."

On Tuesday her manager Larry Rudolph said Britney had gone into rehab voluntarily.