Singer Urban enters rehab clinic
The 38-year-old musician, who married Kidman in June, said in a statement that he "deeply regrets the hurt this has caused Nicole".
It also stated that the Oscar-winning actress was with Urban when he voluntarily entered the facility.
The Grammy winner has previously disclosed an addiction to cocaine.
Postponed
"One can never let one's guard down on recovery, but I'm afraid that I have," the singer's statement continued.
Urban's forthcoming album will be released on 7 November as scheduled, but the singer has postponed all promotional appearances.
He is also unlikely to attend the Country Music Awards next month, where he has been nominated in four categories.
Urban won a Grammy award earlier this year for best male country vocalist for You'll Think of Me, and was named best male singer by the Academy of Country Music for the second year running.
Kidman and Urban, who were both raised in Australia, were married in Sydney and later moved to Nashville, where the singer records.