Conor McGregor -- I'm Back On at UFC 200 ... UFC Hasn't Confirmed

Conor McGregor says he's BACK on the UFC 200 fight card ... claiming he worked out a deal with UFC honchos Dana White and Lorenzo Fertitta ... though UFC has not yet confirmed.

If true, it would be a shocking development considering White had been so adamant about Conor being OFF the card ... since he refused to show up to Vegas this past weekend for promotional obligations.

In fact, White told the media the decision to move on from Conor was final.

Still, McGregor tweeted in the middle of the night ... "Happy to announce that I am BACK on UFC 200! Shout out to @danawhite and @lorenzofertitta on getting this one done for the fans. #Respect"

So far, no word from the UFC -- or White or Fertitta.

Stay tuned ...