"We want to get the party started," Gruden said, per Lindsay Jones of The Athletic.
The team hasn't divulged the wideout's issues officially, although Jones reported that Brown showed a picture of his blistered feet in a since-deleted Instagram story.
Jones wrote the team hoped he'd be back on the field following a Wednesday off day, but Brown has sat out since.
Brown joins Oakland as its top offensive playmaker following nine years with the Pittsburgh Steelers, where he made seven Pro Bowls, scored 79 touchdowns and registered seven 1,000-yard seasons. He led the league in receptions twice and receiving yards twice.
The Raiders face an uphill battle even with Brown on the field, as the AFC West is arguably the NFL's most stacked division. The Kansas City Chiefs and Los Angeles Chargers both went 12-4 in 2018 and look just as strong this season, while the Denver Broncos' defense under new head coach Vic Fangio has the potential to become one of the league's top units.
Oakland reloaded with Brown, wideout Tyrell Williams, rookie running back Josh Jacobs and others, but it's going through a divisional gauntlet this year and will be hard-pressed to come out unscathed.
Still, the team should at least be encouraged that Brown at least seems close to returning to the practice field and gaining much-needed reps with new teammate and quarterback Derek Carr. Plus, the 2019 campaign doesn't start until Sept. 9 against the Denver Broncos, so it's not as if Brown is in danger of missing regular-season action.