Nick Reiner Not Medically Cleared for Court Appearance After Parents' Murders

Nick Reiner -- who was arrested on suspicion of killing his parents Rob and Michele Reiner -- will NOT appear in court today for the first time since their grisly murders ... he doesn't have medical clearance.

Prosecutors were expected to decide whether and how to officially charge Nick with killing his parents ... but that will have to wait, because Nick's defense attorney, Alan Jackson, says his client is not medically cleared to appear in court.

As we first reported ... Nick is on suicide watch at Men's Central Jail in L.A., where he's being held without bail. Jackson said this morning he has not received any filing yet from prosecutors ... and he doesn't believe the court has received any filing either.

TMZ broke the story ... sources told us Nick was acting very strange Saturday night at Conan O'Brien's Christmas party ... not interacting with guests, and his attire was out of place ... it was a pretty ritzy event, but Nick was rolling around in a sweatshirt and seemed high on something. We're told Nick got into a loud argument with Rob at the party, and Rob left with Michele shortly after.

Nick lived at home with his parents, but he opted to check into a hotel at around 4 AM Sunday, using his credit card. The reservation was made for just a day, but Nick never formally checked out.

When the staff came into his room later Sunday morning, they found the shower "full of blood" and blood on the bed.

That afternoon, Rob and Michele were found dead in their Brentwood home with multiple stab wounds. Nick was arrested hours later.