Mark Cuban is adamant that a Mavericks exec did not sexually assault Donnie Nelson's nephew ... saying in a statement that the former Dallas GM's claims are a lie.
Cuban issued the strongly-worded response after 59-year-old Nelson made the allegations in a lawsuit filed in Dallas County.
In the suit, Nelson said his nephew was interested in getting a job in sports and entertainment -- and went to interview with Jason Lutin, Cuban's chief of staff with the Mavericks, about openings in the NBA team's org in 2020.