Every year a big concern heading into training camp and during camp, is injuries. Normally by this time the rookies have had several months of workouts with the team, countless hours learning the playbook, and are entering training camp in the best shape of their lives. Even the veterans enter camp in their best shape that they'll be in all year. Everyone is healthy, fresh, and ready to go.
Even with all that you always have a significant number of players that suffer ankle sprains and hamstring injuries that limit their time in preseason and practice. Now with the players on their own this offseason, especially the rookies, the potential for injury could be significantly higher. Perhaps not quite so much for the veterans because most of them have been working out on their own to get ready and already have a routine that benefits them personally the most. The draft picks though haven't been able to work out with the team and have had to rely on what worked for them in college. The young players are in great shape yes, but an NFL training camp is a whole new experience and with no time to prepare it could become costly for many teams. If for no other reason that the veterans know what it takes to keep their own body in shape and limit the possibility of injuries they may have experienced in the past.
It's just another potential issue resulting from this blasted lockout that's been going on all spring and summer.