We're told the photos were shot at a party in a Vegas hotel room a few weeks before Oscar announced he was back in rehab -- and they appear to show the ex-champ using a rolled up bill to do lines of a white substance off a plate on a table. According to the seller of the pics the substance is cocaine.
Another pic shows De La Hoya leaning back from the table with a grimace on his face.
We've seen the photos -- which are making the rounds to media outlets -- and they offer a possible explanation for why Oscar suddenly checked into rehab just 4 days before what was, arguably, the biggest fight of his career as a boxing promoter ... the Mayweather-Canelo bout.
Sources tell us Oscar was "off the hinges" at the party in the photos, and made the decision to check into rehab shortly after ... realizing just how reckless he'd been that night.
As far as we know, the photos have not yet been purchased.
We're told De La Hoya is aware of the pics. We reached out to his rep ... so far, no word back.