Star wide receiver Antonio Brown missed his second straight day of the Raiders' training camp Friday, and the frustration is really setting in for coach Jon Gruden.

"I think we're all disappointed," Gruden said after practice, per ESPN. "We think he's disappointed. We'd like to get the party started. We'd like to get him out here. He's a big part of the team."

After nine seasons in Pittsburgh, Brown, 31, was acquired in a trade by the Raiders, who signed him to a three-year, $50,125,000 contract. The team's expectations for Brown are high.

But Brown's absence should not be a complete surprise to Gruden. Brown missed much of the Steelers' camp last year, and just last week Gruden said, "I expect a lot more drama from No. 84. I really do."

Well, he's getting it.

Brown, who was well enough to arrive at camp in a hot-air balloon, is out because of a non-football injury. Although there has been no official word on what that injury is, The Athletic reported that Brown was seeing a foot specialist Saturday.

Brown did participate in a walk-through Sunday but was limited Tuesday. Wednesday was an off day.

Brown led the NFL in touchdown receptions last season with 15 and finished with more than 1,200 yards receiving for the sixth consecutive season.