Aaron Hernandez -- Placed In Medical Ward For Safety

Aaron Hernandez is NOT in the general population of jail ... because jail officials are concerned for his safety ... TMZ has learned.

We're told Hernandez -- who has been charged with first degree murder -- has been in the medical ward since his arrival last week. We're told authorities are concerned because of the former Patriots star's celebrity status ... other inmates might try to harm him.

Sources say at the time of this post, jail officials were meeting to decide what to do with Hernandez -- whether to put him in the general population or a more segregated environment.

For now ... Hernandez is in the medical wing ... allowed out of his cell for 1 hour a day.