Rob Reiner gave Jerry O'Connell his first job in "Stand By Me" ... and Jerry told us the late director's murder case is so emotional for him, he may not be able to watch the trial of Rob's son.

We caught up with Jerry in NYC, where he told us all he cares about regarding the case is the Reiner family.

He said, "The only thing I wish for is that this is not a strain on the family ... I just hope it does not become a circus."

Jerry was only 11 years old when he was cast as Vern Tessio in Reiner's 1986 coming-of-age dramedy, giving him a deep personal connection to the family.

"I can't believe I live in a world where Rob Reiner isn't here," Jerry told us. "I feel like a lost a parent."

As you know ... Rob and Michele Reiner were stabbed to death at their home on December 14. Their son Nick Reiner was charged with their murders and yesterday pleaded not guilty.

We also learned Nick's siblings, Romy and Jake, are no longer paying for Nick's legal fees.

One source told TMZ, the way Jake and Romy see it ... "Nick's defense is Nick's defense. They're not involved."