Shady opened up about the leaked snippet of "Things Get Worse" during a SiriusXM interview Monday, saying he doesn't have any recollection of recording the verse in which he raps that he sides with Chris Brown ... this shortly after CB assaulted Rihanna in 2009.

Em's controversial verse -- "I'm not playing, Rihanna, where'd you get the VD at?/ Let me add my two cents/ Of course I side with Chris Brown/ I'd beat a b***** down too/ If she gave my d*** an itch now." He scrapped it from the final version of his 2019 collab with B.o.B.

The rapper says he told his manager after the leak that he had no idea how someone got it, but also claims ... "I have zero recollection of even remembering doing that verse." Eminem added ... "The rhyme scheme doesn't even sound, like, familiar to me. So I was caught off guard, too. I was like, 'What the f***?! I said that?'"

Shady says it's no excuse, and calls it "f***ing stupid" of him to record the verse, but claims at the time he was re-learning how to rap due to his addiction issues. He says he believes he just went with it because it rhymed ... but adds he should have thought better of it.

On "Zeus," Eminem addresses Rihanna directly with the lyrics ... "And wholeheartedly, apologies, Rihanna/ For that song that leaked, I'm sorry, Ri/ It wasn't meant to cause you grief."