Lisa Vanderpump Still Mum On Rachel Leviss' Return to 'Vanderpump Rules'

Rachel Leviss' big return to "Vanderpump Rules" has been mostly shrouded in mystery ... but surely Lisa Vanderpump would help give some answers, right? Think again.

We got Lisa on the TMZ Celebrity Tour in WeHo Thursday ... and as we chatted at a red light about her recent Emmy nominations, we asked her the million-dollar question -- is RL comin' back or not??

Of course, Lisa's keeping a tight lip on the whole situation ... playfully making her big escape thanks to a perfectly-timed green light.

Jokes aside, the 'VPR' matriarch has gotta know something about Rachel's return, but she ain't spilling the tea any time soon. TMZ broke the story, Rachel's actually bound by her contract with Bravo to join the cast for season 11, but she's still in negotiations -- possibly for a higher rate.

Remember, Rachel left her mental health facility earlier this month after checking herself in back in April ... and has been MIA while production picked back up for 'VPR.' Nothing's been said about how she was doing while away -- even Tom Sandoval wouldn't blab.

If we were betting, it seems increasingly unlikely Rachel will return to the show ... they're halfway through shooting Season 11, and it's gonna be hard to integrate her into the storylines.