Michael Jackson's eldest son Prince -- an eyewitness to the horrific scene in the bedroom where his father lost his life -- does not want to testify in the Conrad Murray trial, but he's telling family he'll do what needs to be done to get justice for his departed dad.

Sources close to Prince tell TMZ ... the 14-year-old is "nervous" and worried that if he's called to the stand he might get flustered and "mess up."

We're told if Prince is called by prosecutors ... Katherine will ask her lawyers to request that the entire courtroom be cleared during his testimony. Judge Michael Pastor almost certainly will prohibit the media from training a camera on Prince, but it's unlikely he'll clear the courtroom.

As we previously reported, Prince is on the prosecution's witness list, since Dr. Murray summoned Prince to the bedroom for help during the emergency. When Prince arrived, he dissolved into tears.

The trial starts today. We'll be livestreaming opening statements.