Jay-Z is being sued by a former Roc Nation Sports boxer -- who blames Hova and the company for the severe brain injuries he suffered after taking 3 fights in 79 days.
The boxer behind the lawsuit is Daniel Franco -- who claims he signed a deal with Roc Nation Sports back in 2015 ... and won his first 5 fights with Jay-Z's company.
But, the problems started in March 2017 ... Franco claims he came down with a bad flu before a big fight which sidelined him from training for 3 weeks.