'Rob & Chyna' Season Two Is Officially Iffy

Rob Kardashian and Blac Chyna's TV career together is looking short and NOT sweet -- season 2 of their show is now hanging by a thread.

Production sources on "Rob & Chyna" tell TMZ ... E! execs haven't ordered a 2nd season yet, and a big part of the problem is they can't get the couple to shoot together. As we've reported, Rob's become a hermit again and we're told that's giving the bosses cold feet. Understandably, they're worried they won't get a full season out of him.

Obviously, a sophomore season could get huge ratings with so much drama, plus a baby and possibly a wedding around the corner ... if Rob's on board, and we're told that's a BIG if right now. Not to mention the season airing now is doing very well.

Our sources say honchos think Chyna's TV gold, and would consider working with her solo on a different show -- but if her fiancé remains MIA ... "Rob & Chyna" will die on the vine.