McGregor hasn't fought in the Octagon since Nov. 2016 when he defeated Eddie Alvarez at UFC 205. Of course, he boxed Floyd Mayweather in August 2017 ... and reportedly made around $100 mil.

Floyd had said he wants his next fight to be in the Octagon -- but he hasn't signed a contract and even Dana White has said he has no idea when the Irishman will fight again ... if ever.

So, when we saw Faber out in Hollywood with Patrick Schwarzenegger ... we asked if he knows anything!

"I don't know what the f*ck's up with Conor ... that's my boy," Faber told TMZ Sports.