NAPA, Calif. -- Another day, another day off for Antonio Brown, and Oakland Raiders coach Jon Gruden acknowledged that frustration is mounting with his star receiver missing so much time so early in his first training camp with the team.

"I think we're all disappointed," Gruden said after practice on Friday. "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.

"But for the time being we're going to continue to work hard and we're seeing the development of some other receivers we're excited about."

Brown, who began camp on the non-football injury list with an undisclosed injury, participated in a pre-practice walk-through on Sunday and was limited in practice on Tuesday. That night, he posted a picture of the bottom of his feet, which were blistered and peeling. He has not been seen on the practice field the past two days, after Wednesday's off day.

And while Gruden praised the efforts of receivers Tyrell Williams, Marcell Ateman and J.J. Nelson and tight end Darren Waller in Brown's absence, Gruden would not call the pass-catchers stepping up a blessing in disguise.

"I'm not going to get into all that," Gruden said. "I want the guy out here as soon as possible. I'd like him to never leave and stay in the huddle every play. But life goes on and you've got to continue to work and the other guys got to take advantage of these opportunities, and so far, they have."

Raiders special teams coach Rich Bisaccia said he would like to see Brown field a few punts upon his return. Brown last returned punts in 2017, for the Pittsburgh Steelers, and has returned 186 punts for 1,759 yards and four touchdowns in his career.

"I think when Antonio certainly comes back to practice we're going to get him back catching and put him in a situation where hopefully he's in a backup role, or who knows, there could be two guys back there together," Bisaccia said. "A lot of different things can happen. I know he didn't return last year and I've played against him when he was the return guy. He's certainly capable of doing that. But our intention is certainly to use him on offense and have a guy return and him possibly be the backup."