ENGLEWOOD, Colo. — Outside linebacker Randy Gregory and offensive lineman Billy Turner remain on the Physically Unable to Perform (PUP) list, but Head Coach Nathaniel Hackett said that they could be ready to play by the start of the season.

"They're right on track, and we want those guys for Week 1," Hackett said. "That's what we're aiming for."

Gregory and Turner have exclusively worked on a side field during training camp, and neither player participated in the offseason program.

Safety Kareem Jackson returned to practice after a rest day on Thursday, while outside linebacker Christopher Allen (foot) did limited work in his return to the field.

Wide receiver Kendall Hinton (knee), wide receiver Tyrie Cleveland (throat), cornerback K'Waun Williams (knee), safety Caden Sterns (hip) and defensive tackle D.J. Jones (back/rest) did not practice.

Hackett did not provide a specific timetable for Williams' return, but said they will continue to rehab him and hopes he will return "sooner than later."

'We want to be so careful, especially with some of the older guys to make sure that they're brought back in the fold the right way," Hackett said. "[Williams is] such a valuable person for us, going against him and the things he's done. So we're just going to work him back in the right way."

Safeties J.R. Reed and P.J. Locke participated in practice after being attended to by trainers during Thursday's practice.