Regarding Minnifield's injury, there was this scout report from April 25, 2012:
Former Virginia defensive back Chase Minnifield is recovering slower than expected from his January knee arthroscopy, which reports indicate included a microfracture procedure, but he expects it will lead to an improved final result. "I am getting better every day and I only have trace swelling," Minnifield told NFLDraftScout.com. "My doctor, James Andrews, made a report that all NFL teams received. They know. I am not 100 percent, but I will be."
Being on the PUP list means a player has to sit out the first six games of the season of the regular season [Editor's Note: if they're not activated during training camp, which a coach can do at any time.]
PUP rules differ for training camp and regular season. Via TST:
Only players who cannot practice at the start of training camp can be placed on the PUP list. Those players can be moved to the active roster at any time. If [a player] begins the season on the PUP list, he cannot practice or play for at least six weeks. PUP players can begin practicing after six weeks, and their teams have three weeks from the time the player starts practicing to add them to the active roster. If the player does not practice within that three week window, they have to be left on the PUP list the entire season.