Leonardo DiCaprio Sues -- I Didn't Knock Up Rihanna

Leonardo DiCaprio may be dating Rihanna, and he's most likely even banging Rihanna -- but he absolutely did not get her pregnant ... according to a lawsuit he's filed against a French magazine.

Leo filed the suit against Oops! for its May 28 cover story ... which declares that Leo knocked up RiRi, and will not recognize the baby as his. In the docs, Leo's lawyer calls the story "pure fantasy."

Here's what's odd -- sources close to Leo tell TMZ ... his team recently contacted Oops! and informed the people running the magazine that the story was false. We're told the mag's response went something like ... yeah, we know and we don't care -- except in French.

One source tells us it's almost like the magazine wanted to be sued, possibly just to gain publicity.