The American Pie star was driving through Los Angeles when his car was pulled over by police last month (Jun10).
He was arrested after failing a sobriety test and was later charged with two misdemeanours which could land him a stint in jail.
Klein checked into the Cirque Lodge rehab facility in Utah, which previously housed Lindsay Lohan, to seek professional help for his problems. He signed up for a 30-day program and his rep, Jaime Primak, has now confirmed he will be staying a while longer.
Primak tells People.com, “Chris, along with his support team, has decided to extend his treatment. He is doing fantastic and is optimistic about his future. He thanks everyone for their continued support.”