Mack failed to show up for mandatory minicamp and could hold out of training camp as he seeks a lucrative contract extension.
"That might be the toughest decision I have to figure out right now," Gruden said, via ESPN. "We're not the only team that's faced with that. It's tough. It's part of this business and we'll just keep our fingers crossed."
A three-time Pro Bowl selection and 2016 NFL Defensive Player of the Year, Mack is set to make $13.846 million this season in the fifth-year option of his rookie contract. The 27-year-old reportedly is looking to become among the highest-paid non-quarterbacks in the league.
Mack recorded 78 tackles and 10.5 sacks in 16 games last season. He has 303 tackles and 40.5 sacks in 64 career contests since being selected by the Raiders with the fifth overall pick of the 2014 NFL Draft.