Calvin Klein and Nick Gruber.

Addiction problems ... Calvin Klein and Nick Gruber.

Calvin Klein's boyfriend has reportedly checked into rehab following his recent arrest.

Former porn star Nick Gruber, 22, who is in an on/off relationship with the 69-year-old designer, was taken into custody by police recently after he allegedly punched a man who was partying at his flat.

Police also found cocaine on Gruber and he was arraigned on a felony charge of drug possession and misdemeanours of assault and resisting arrest.

The incident took place in his penthouse in New York City, which is said to be paid for by Klein.

It's now been suggested Gruber has gone to a treatment facility to get help.

"A spy tells us Gruber was seen leaving his luxury 666 Greenwich St building 'with a wheelie suitcase' and talking about his impending trip to rehab yesterday," reports New York Post.

Gruber was reportedly worried there would be photographers swarming his building, although none were present when he left.

The young man has already got in touch with a lawyer, with Ben Brafman enlisted to work for him. Last night the lawyer made no comment on the latest rumours.

Klein has been open about his own struggles with addiction. He has battled problems with prescription drugs and alcohol in the past, receiving rehab treatment several times before.

CM