'Affluenza teen' Ethan Couch to be released as his lawyers argue testing will show he didn't violate parole Couch, 22, was on probation after he was released from jail in April 2018.

Ethan Couch, the Texas man known for claiming "affluenza" as part of his defense in a fatal DUI crash, will undergo additional testing to prove that he did not violate his parole, his lawyers said Friday.

Couch, 22, had been on probation since being released from jail in April 2018 after serving 720 days for earlier violating his probation in connection with a drunken-driving accident that killed four people and injured several others.

He was back in Tarrant County Jail on Thursday after he tested positive for THC in a mandatory drug screening that was part of his probation, court documents showed.

His lawyers said they expect he will be released Friday or Monday, pending further investigation and additional testing.

"We are optimistic the additional testing will verify Ethan has not knowingly and voluntarily used alcohol, THC, or any other prohibited substance since being released from custody more than 20 months ago," attorneys Scott Brown and Reagan Wynn said in a statement to ABC News.

"Ethan is committed to his sobriety and to remaining compliant with all of the terms and conditions imposed by the Court," the statement continued.

Couch was ordered to be held without bail after he tested positive on Thursday.

At his 2013 trial, Couch was found guilty of four counts of involuntary manslaughter and initially sentenced to 10 years of probation and time in a rehabilitation center.

The case garnered national attention when, during the sentencing phase, a psychologist testified that the then 16-year-old Couch was a product of "affluenza" -- a term he used to describe Couch's irresponsible lifestyle associated with his affluent upbringing -- and that irresponsible parenting had "strongly enabled" the accident, even though Couch had a blood-alcohol level three times the legal limit on the night of the crash.

While on probation in 2015, Couch failed to show up to a check-in with his probation officer, sparking a manhunt. Authorities discovered he'd fled to Mexico with his mother, Tonya Couch.

Couch and his mother were arrested in Puerto Vallarta after U.S. Marshals and other American law enforcement agencies pursued them for nearly two weeks.

After being extradited to the U.S., Couch was sentenced to 720 days in jail for violating the terms of his probation -- 180 days for each victim.

Meanwhile, Tonya Couch was charged with hindering apprehension of a known felon and money laundering, but released on bond. Her case is still pending.

Late Thursday, attorneys for Ethan Couch released a statement that read, in part: "Based on the limited information available to us, the only basis for the issuance of the warrant is that Ethan was allegedly 'positive' for THC on a Substance Abuse Test Patch. Ethan has been intensely monitored for alcohol and illegal substance use, including constantly wearing the required patch, for more than 20 months and has never been positive for the use of any substance before. We cannot make any further statement until we have the opportunity to conduct an investigation to determine if, in fact, Ethan ingested THC and, if so, if it was a voluntary act on his part."

ABC News' Allie Yang and Lisa Soloway contributed to this report.