Chad Johnson -- Yes, The Sex Tape is Real ... But I Didn't Leak it

Chad Johnson acknowledges ... a sex tape which appears to feature the former NFL star -- along with TWO female friends -- is REAL ... but Chad insists he never wanted the footage to go public.

Sources close to Johnson ... ha, Johnson ... tell TMZ the tape was shot roughly 3 years ago in a hotel room in Florida.

We're told Chad has no idea how the tape leaked to the Internet ... but insists he wasn't behind it ... and now he's exploring his legal options in hopes of having the tape removed from the web ASAP.

So far, it doesn't appear the entire video has made it's way into cyberspace -- only bits and pieces -- but we're told the entire tape is "substantial in length" ... ha, substantial in length.