Given that the players and teams are separated by the current NFL Lockout, it's hard to get completely accurate information about the physical well-being of the players. Players are often pretty low key about their injury issues and if there isn't an official team PR representative passing along information it's possible we'd never find out what's going on with the players. Some of the 49ers offensive players have shown just how true that is.
Eric Heitmann has been dealing with a neck injury since last season. Last I read he was rehabbing his neck at Stanford but had not been cleared to practice yet. If he's ready to go by training camp then I suppose his missing these training camps won't be that big a deal. Neck injuries are serious business so it makes sense that he would wait until he's 100% before he starts practicing again.
The issue of real significance at the moment would be the foot issues faced by Michael Crabtree. Prior to the 2009 NFL Draft, he had surgery on his left foot after suffering a stress fracture. During this month's previous 49ers minicamp, there were some issues with new shoes causing problems and Crabtree did not take part in the on-field work. The latest minicamp has begun and although he is in attendance, he's not getting involved in the route running as he still has some concerns about his foot.
Given that it's been two years since the surgery this is cause for at least a little bit of concern. Some great athletes in sports have been felled by feet injuries. The most well known is probably Bill Walton, who dealt with foot injuries throughout his NBA career. There are distinct differences between an NFL and NBA career, but for a wide receiver who is using his feet so prominently in making cuts and racing past defensive backs, I can see how a foot injury could be a significant problem.
The other injury "issue" belongs to wide receiver Kyle Williams. He dealt with hamstring issues in the past and pulled up with a hamstring problem in the last minicamp. Williams took part in practice today but left practice early in order to be cautious about the hamstring.
If you see any other specific injury updates, feel free to post them in the comments.