Erik Menendez is not in prison right now … he is in a nearby hospital being treated for kidney stones, and it’s possible he will not return … sources with direct knowledge tell TMZ.

We broke the story … Erik is being treated with what his lawyer Mark Geragos called a “serious medical condition.” We have confirmed that the condition is kidney stones.

The California Department of Corrections and Rehabilitation confirms Erik was transported to an outside medical facility Friday … and we’re told he is currently in fair condition.

Our sources say California Governor Gavin Newsom is currently reviewing Erik’s change in medical condition to determine if a “prison furlough” is appropriate.

It’s unclear how long such a furlough would last … it could be only until the kidney stones pass, but because Erik’s upcoming parole hearing is only a month away, Newsom could cut Erik a major break where he would not have to return to prison pending parole board review.

Erik and Lyle Menendez are scheduled for a parole board hearing August 22 … and Newsom has indicated he’s sympathetic to granting both Erik and Lyle clemency.