Sources familiar with the case tell TMZ ... Dr. Murray's team will argue that at the time of his death, Jackson's body was failing him ... partly because he was "driven over the edge" by AEG to rehearse for his upcoming tour.
We're told Murray's lawyers will call witnesses to testify that Jackson was not showing up for rehearsals -- and when he did show, he was exhibiting "clear signs" of failing health.
The upshot of the defense ... even if jurors believe Dr. Murray administered the fatal dose of Propofol, Jackson was already in failing health.
But as TMZ has already reported ... Dr. Murray's lawyers will argue Jackson himself administered the fatal dose of Propofol to himself when Murray was out of the room.
The trial begins in April.