Sophie Rain says a basketball star offered her a bag to take her virginity ... but, she's not outing the dude by name.

We caught up with the popular OnlyFans creator outside Gravitas -- a members-only club in Beverly Hills -- on Friday ... and we had to ask her about which baller made the offer.

If you haven't seen it ... Rain shared an alleged message she received from an athlete making the offer -- but she says she turned him down.

Check out our interview ... Rain won't tell us who the dude is but admits he plays basketball. That's all we've got to go on -- which narrows it down, but certainly not enough to make a guess.

Rain says the dude ghosted her when she turned him down ... but he didn't get pushy at least.

It's not surprising Rain said no ... she claims to make more than $40 million a year on OF -- so she doesn't have to sell her virginity to the highest bidder just to pay her bills.

We also asked if Sophie ever heard anything about her offer to collaborate on OF with Cardi B ... watch the clip all the way through to hear her answer.

Bottom line ... ballers need to keep their balls to themselves -- Sophie's not interested.