"He's not the only one, but obviously you want your players to come in and be ready to go," coach Doug Marrone said Sunday. "We're here for a long period of time and we'll make up for it."
Dareus remained on the active/non-football injury list as the Bills held their first training camp practice Sunday evening.
Dareus is expected to report to camp on Monday, but won't re-take the conditioning test until Thursday, at the earliest, a team source told ESPN's Sal Paolantonio.
It's the latest setback for Dareus, who was arrested twice this offseason and could face an NFL-imposed suspension.
Marrone, however, was optimistic about Dareus.
"He'll be in shape and ready to play," Marrone said. "Right now he needs to focus on getting himself ready, getting himself on the field, and focus on football.
"I think that's what he'll be ready to do and that's been my conversations with him."
Bills' Dareus Failed Conditioning Test
Mike Rodak discusses how much of an impact Marcell Dareus' failed conditioning test will have on his status with the team.