Lynch defeated Rousey and Charlotte Flair in the main event Sunday night -- earning both the WWE Raw AND Smackdown belts ... leading Conor to dub her the sport's first "Champ Champ."

"Congrats to Irelands Becky Lynch, the WWE’s first Champ Champ," McGregor wrote.

"Wow! What a match these ladies put on! Ronda Rousey is something special in that ring, as is Charlotte Flair of the Flair dynasty!"

That's when the tease came ...

"Stephanie McMahon you are right, I could not do what these athletes do. Or could I... "

McGregor hasn't exactly had the best relationship with WWE -- in 2016, he went off on a bunch of the wrestlers as "p**sies" who could never win a real fist fight.

"For the most part, those WWE guys are p**sies," McGregor said at the time ... "They're messed up p**sies if you ask me."

He did, however, praise Vince McMahon and Triple H at the time.

So, will he or won't he???

We recently shot Steph McMahon who told us she would love to sign Conor to a WWE contract ... if he's serious about wanting to get in the ring.

Conor's future seems to be a mystery -- he "retired" from MMA in a tweet last month ... but then told Khabib Nurmagomedov he would see him back in the Octagon.