Conor McGregor didn’t step up to fight Khabib Nurmagomedov at UFC 223, but Dana White says it’s a “100%” certainty the Irishman fights in the Octagon again -- THIS YEAR.

But, bad news for Conor – he won’t be coming back a UFC champion.

Dana just dropped the bombshell at the news conference for UFC 223 in Brooklyn .... confirming McGregor will continue his MMA career sometime in 2018.

But, as the UFC prez has told us in the past, Conor's gonna have to drop his 155-pound belt as soon as Khabib and Max Holloway get it on at 223.

As for McGregor's opponent -- Dana didn't say. But, the winner of Khabib vs. Max for the UFC lightweight title would make sense as Conor’s matchup.

Khabib and Max also got in their shots at the Q&A sesh ... with Khabib mocking Holloway for thinking he stands a chance against him.