A pushing incident between Lindsay Lohan and a staffer at the Betty Ford Center in southern California has escalated into what local police are investigating as a misdemeanor battery case.

"The incident involved Lindsay Lohan and another female adult who was a staff member at the location," said a statement attributed to both the Riverside County Sheriff's Department and the Palm Desert Police Department. "The incident is being investigated as a misdemeanor not committed in the presence of a peace officer. Therefore, no one was arrested at the scene. The investigation is currently ongoing."

With fewer than two weeks remaining in Lohan's court-ordered substance-abuse rehabilitation, the "Mean Girls" star had been returning to a Center-affiliated sober house in the early-morning hours of Dec. 12, after a night out with roommates, said TMZ.com.

There, as the site claimed Lohan told friends afterward, a female staff member "unfairly" scolded her, demanded she take a drug/alcohol test and, during a heated exchanged, put her hands on the starlet. Lohan, said TMZ, told the woman "Take your hands off of me" and then "pushed back."

The police statement said that "at 1:03 a.m. officers from the Palm Desert Police Department conducted a battery investigation."

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Lohan's attorney, Shawn Chapman Holley, is expected to release a statement today .

Lohan, 24, is in inpatient drug and alcohol rehab at the Betty Ford Center through at least Jan. 3, the date imposed by a Los Angeles Superior Court Judge Elden S. Fox in an October probation hearing stemming from her 2007 DUI convictions. She is scheduled to return to court in late February.