According to Howard Balzer of the SportsXchange five Patriots rookies failed their physicals upon reporting to the team on Thursday.
WR Jeremy Ebert was the only draft pick of the group. The other four were undrafted free agents: DL Justin Francis, OL Jeremiah Warren, WR Matt Roark and OL Markus Zusevics.
According to Balzer, Ebert was placed on the active PUP (physically unable to perform) list, while the others were placed on active NFI (non-football injury).
Part of the physical to open camp is the team's conditioning run. Failing the conditioning run would be a failed physical, although an actual injury is also obviously a possibility. For example Zusevics suffered a torn pec at the Combine and was limited to simply observing practice during spring OTAs and mini-camp. ESPN Boston reported that Ebert was limited by a leg injury during mini-camp.
The players can be removed from PUP or NFI at any point during the summer and preseason at whatever point they pass their physical.