NAPA, Calif. – Oakland Raiders cornerback D.J. Hayden, who missed most of the team's offseason training programs after rolling his right ankle and foot on the third day of organized team activities in May, will be placed on the Physically Unable to Perform list and miss the start of training camp, coach Dennis Allen said Thursday.

Allen, speaking to five media outlets and the team's Web Site over lunch at the Napa Valley Marriott Hotel & Spa, said an initial MRI of Hayden's ankle in the immediate aftermath of the injury showed no damage. But when the injury did not heal in a timely fashion, a second MRI revealed a stress fracture in the foot and Hayden underwent surgery just after the team's mandatory minicamp June 17-19.

There is no timetable for Hayden's return, though Allen said some players have returned in as few as four weeks time after a similar procedure.

"It's disappointing, both for him and for me," Allen said, "because he's a guy that we're counting on being able to step up and help us this year and he's a young player and he needs the reps."

With the Raiders having only 13 practices in Napa before they break camp and head to Oxnard for a pair of practices on Aug. 12 and 13, it is likely Hayden will miss camp.

Hayden, the Raiders' top draft pick in 2013 at No. 12 overall despite suffering a near-fatal heart injury as a college senior at Houston, had an injury-filled rookie NFL season. He missed a significant portion of his training camp recovering from surgery to remove resultant scar tissue in his abdomen and then played in eight games before going on season-ending Injured Reserve after undergoing sports hernia surgery.

He had one interception, which clinched the Raiders' home victory over the San Diego Chargers on Oct. 6, 2013, a forced fumble and 29 tackles, 23 solo, last season.

Hayden had been penciled in as the first-team right cornerback and, after that first OTA practice on May 27, he said he was "light years" ahead of where he had been a year earlier.

With Hayden's situation, Carlos Rogers and Tarell Brown are Oakland's top two corners a day before the Raiders' first practice. Plus, Allen mentioned the progress of seventh-round draft pick TJ Carrie and fourth-year defensive back Chimdi Chekwa as potential corners in a nickel package. Allen did not say if Hayden's situation put the Raiders in the market for another cornerback.

"Is it a setback? Yeah, it's a setback," Allen said of Hayden. "Is it something that's going to keep him from being able to contribute this year? I certainly hope not. But that will be determined by how fast he's able to recover, how fast he's able to get out on the field. And once he's out on the field, what's he able to do? How's he able to perform?

"It's really about, how does the foot respond and when's he able to be pain free or we can begin to get him out there and start him running and start getting him into football activity."

And Hayden's mindset?

"I think he's frustrated but I don't think he's in any state of despair or anything like that," Allen said. "I think he understands he's got another challenge he's got to overcome … the kid wants to be out there, he wants to play. It's just been unfortunate that he's had some injuries that have kept him from being able to do that."