Robbie Williams is facing a law suit from the rehab centre that treated him recently, reports DigitalSpy.
The singer angered staff at the Cottonwood de Tucson centre by declaring that the clinic was "worse than a concentration camp" after he checked out early.
A source at the clinic told the Daily Star Sunday: "We're one of the most respected rehabs in the world and what this man has said is outrageous. Board members have taken legal advice and have been told they have a defamation case against him. Everyone on staff is backing their action 100%."
Robbie checked into the centre last month after admitting that he was addicted to prescription pills.
Meanwhile, Black Eyed Peas star Fergie has revealed that Robbie Williams is "doing great" following his stint in rehab.
The singer met Robbie at a Los Angeles party last week and is certain that he will bounce back from his recent troubles.
"We've all faced our demons at some point. I feel I can relate to him. In this day and age it seems everyone is going crazy," Fergie explained.
"But Robbie is doing great. He's such a charmer. He'll come back stronger from all this. That boy knows how to pack out arenas."