Lohan has been undergoing treatment at the Ranch Mirage rehab since Sept. 24.
Judge Elden Fox Friday said he found the "Mean Girls" and "Freaky Friday" star had again violated the terms of her probation in a 2007 driving-under-the-influence case, The Los Angeles Times reported. Fox ordered her to continue her treatment instead of having her serve time in jail for testing positive for drugs, however.
After she leaves rehab in early January, she is to undergo random testing until her Feb. 25 court date, the Times said.
"I'm serious about that (date)," Fox told Lohan. "You're staying there past the new year and there's a reason for that. I'm not going to be manipulated."
Fox also warned Lohan that if she violates the terms of her probation again, he will follow the recommendation of prosecutors and sentence her to 180 days in jail, the newspaper said.