The actress reportedly completed her court-ordered rehabilitation at the Betty Ford Center on Monday.
Sheriff's investigators said a two-week investigation shows she violated probation when she got into a skirmish with a clinic worker.
Lohan allegedly violated curfew at the clinic on Dec. 12 and refused Dawn Holland's request to take a breathalyzer test. The argument resulted in Lohan calling 911. But when the staff member tried to pick up another phone, Lohan allegedly ripped it out of her hand and injured Holland's wrist.
Holland initially pressed charges but later dropped them.
Holland's attorney, Keith Davidson, said his client "doesn't want to go forward with pressing charges and believes the incident was a minor one."
A Beverly Hills judge threatened jail if Lohan violated probation.
Lohan's attorney, Shawn Chapman Holley, said 'The fact that the Palm Desert Police Department went outside this limited role to issue a press statement expressing its opinion about what should happen in Ms. Lohan's case is highly unusual and deeply troubling."
The case now goes to the district attorney and the Los Angeles County Probation Department.
Lohan has been receiving treatment at Betty Ford since last September. A judge overseeing her probation for her three-and-a-half-year-old drunken driving case required Lohan to remain at the rehab center until Monday.
On New Year's Day, the "Mean Girls" star posted a message on her Twitter account.
"Today is the first day of the rest of my life," it said. '"The future depends on what we do in the present.' -Mahatma Gandhi...One step at a time..."
Lohan, who is expected back in court on Feb. 25, is looking at six months in jail if she is found to have violated her probation.
Holland was let go from Betty Ford after speaking publicly about the incident. Betty Ford said Holland violated their patient confidentiality clause.
The Associated Press contributed to this report.