9:58 AM PT -- A rep for Sports Trinity -- which represents the Qatari investors -- tells TMZ Sports, "Sport Trinity never made an offer of this nature to Jerome Williams."

"His statements to TMZ are completely false and illogical, particularly as Sport Trinity is the largest investor in the BIG3 Basketball league."

Ex-NBA player Jerome Williams -- aka the Junk Yard Dog -- says he was offered $25 MILLION to start a rival 3-on-3 basketball league last year ... while he was still playing for the BIG3 league.

But the craziest part ... Williams claims the people behind the offer were the same Qatari investors who already owned a piece of the BIG3.

Of course, the BIG3 is suing the Qataris for more than $1 BILLION -- claiming they never made good on their $5 million investment ... and then threatened a league owner when asked for the money.

Now, Williams tells TMZ Sports he believes the Qataris were essentially trying to sabotage the BIG3 by wooing players like himself to ditch Ice Cube and Jeff Kwatinetz and join a rival venture.

"I'm JYD! It's not the first time I've turned down $25 million."

Williams says the Qataris flew key people associated with the BIG3 to St. Tropez and let them drive fancy cars ... but ultimately, the plan failed.

There's more ...

Jerome also has a message for his "good friend" Roger Mason -- former BIG 3 commissioner -- who's also suing the BIG3 and has a friendship with the Qataris.

"I would run fast and far away from these guys."

We reached out to Sports Trinity -- which represents the Qatari investors -- but were unable to get a comment.