Lindsay Lohan had consumed alcohol on the night she was accused of attacking a Betty Ford Center employee.
According to a probation report, released yesterday, the troubled actress failed a random alcohol test after sneaking out of the rehab facility, which is located on the Rancho Mirage, in California, one night last December.
The report cited police interviews with restaurant and nightclub employees who testified they had seen her drinking.
The 'Gotti: Three Generations' actress was also accused of criminal battery against Dawn Holland, an employee of the centre, on the same night but charges were later dropped due to lack of evidence.
Lindsay underwent a three-month court-ordered programme at the rehabilitation clinic after breaching the terms of her probation, stemming from her 2007 arrest for driving under the influence (DUI).
After completing her stay in January, the 24-year-old star said she felt "great" and was "focusing on the one thing I know I need to put first in my life, which is my recovery."
Lindsay's troubles continued, however, as soon after leaving the centre she was accused of stealing a necklace from upmarket jeweller Kamofie & Co.
According to the probation report, she also tested positive for alcohol in February, one week after her assistant gave the allegedly stolen necklace to police.
Of this incident, the report stated: "The probation officer believes that substance abuse is the root of the defendant's problems."
The jewellery theft case was resolved this week, with Lindsay pleading no contest to misdemeanour theft.
She was sentenced to undertake three years probation, serve 120 days in jail, complete 40 hours of community service, undergo psychological counselling, pay fines of $180 and attend a scheme to help shoplifters.
In a subsequent statement, Lindsay said: "I am glad to be able to put this past me and move on with my life and my career. I support the judge's decision and hold myself accountable for being in this situation."