Jon Gruden said this week he expects "more drama" involving Antonio Brown ... and guess what -- he got it.
The Oakland Raiders superstar has been sued by his famous personal trainer who claims the WR stiffed him out of thousands of dollars stemming from a week-long off-season workout program.
The man behind the suit is Sean Pena -- who's trained pro athletes like NFL star Darius Leonard.
Pena somehow connected with Antonio Brown in 2019 -- and the two started working out together.
Pena claims AB had him fly up to NorCal for one week of hardcore training in April -- and he even posted footage of the two grinding it out in the gym at the University of California Berkeley.
They did everything from foot speed drills to weight training, balance work and water-resistance work in a pool. The sessions actually looked pretty intense.
But, when it came time to pay up, according to the lawsuit ... Brown never ponied up the dough.
According to court docs, obtained by TMZ Sports, Pena is demanding $7,194.81 for "unpaid therapy and training services; agreed-upon reimbursement for hotels, airfare, rental car, and [miscellaneous fees], in addition to late penalties disclosed on accepted invoice."
The case has already been assigned a trial date for October -- which will go down unless the two sides can reach a settlement before that.
When reached for comment, Brown's attorney, Darren Heitner, tells TMZ Sports ... "Mr. Brown has already paid the Plaintiff everything that he was due. The Plaintiff has no foundation for coming after Mr. Brown, and we will ensure that this case disposed of quickly."
FYI, Brown signed a 3-year, $50 MILLION contract with the Raiders during the off-season.
12:04 PM PT -- Pena's attorney, Michael D. Kolodzi, provided TMZ Sports the following statement, saying ... “Antonio Brown and his attorney have intentionally chosen to ignore Pena’s claim for unpaid trainer services."
"Indeed, Pena is one of many trainers that Brown has stiffed. It is a repeated pattern of conduct with Brown which assuredly will be brought to the attention of the Court."
"To the chagrin of his Florida counsel, Brown will, in fact, have to personally appear in an Alameda County Court and argue his defense of this case. There are no attorneys allowed in small claims in California."
"Thus, his attorney has no power or ability to ‘ensure that this case is disposed of quickly.’ Such a statement is without merit, completely nonsensical, and demonstrates a profound lack of knowledge of California jurispridence.“