ENGLEWOOD, Colo. -- Chris Harris Jr. will be the only Bronco to open training camp on the preseason physically unable to perform list, but the fourth-year cornerback is still on track to return by the start of the regular season, Head Coach John Fox said.

"I'm not a fortune teller. But our hope is yes," said Fox. "But we'll just take it day-to-day."

Harris' recovery is on schedule, Fox said, and had no setback that led to the PUP designation. What holds him back is the occurrence of his torn anterior cruciate ligament: on Jan. 12, barely six months ago.

"I'm not sure I've ever seen a guy work any harder to rehab," Fox said.

Harris being the sole player on the PUP list means that defensive tackle Kevin Vickerson and linebacker Von Miller will open training camp on the active roster. Both spent their offseason rehabilitating from injuries suffered in the final six weeks of the 2013 season.

Miller took part in individual drills during organized team activities. Vickerson was not cleared to run until June, but said then that he was "trying to push toward training camp."

Based on Wednesday's status, Vickerson's quest was successful. But Fox acknowledged that some players will have "limitations" when camp begins.

"We'll be smart, even with our healthy guys," he said. "I think when you look around the league and look at the start of training camp opening up around the league, there's been some injuries that occur very early. So we'll be working hard, but we'll be working smart."

Harris can be on the preseason PUP list until he takes part in a practice drill, at which point he must be moved to the active roster. If he remains on the PUP list into the regular season, he would be forced to sit out the first six games.