According to TMZ Sports, court documents say Pena is seeking $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."
Pena alleges that Brown never paid him after he flew to Northern California in April to work with the seven-time Pro Bowler for a week.
Brown's attorney, Darren Heitner, told TMZ Sports that Brown paid for the services provided by Pena: "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."
The case is set to go to trial in October.
In July, Brown reached a settlement in a different case stemming from a 2018 incident in which he allegedly nearly hit a toddler with furniture he threw off a balcony. As part of the settlement, Brown had to contribute to the child's college fund and make a charitable donation.
The four-time first-team All-Pro figures to be a focal point in Oakland's offense for the next few seasons after signing a new three-year, $50.125 million deal with the Raiders.
In 2019, Brown will look to help turn around a Raiders team that is just 10-22 combined over the past two seasons.