Earlier today, ESPN's Adam Schefter tweeted that
Chargers QB Philip Rivers, who missed practice Wednesday, is battling a back injury that is bigger than people realize, per league source.
A couple of observations:
Schefter cited a LEAGUE source, not a TEAM source. If the report is accurate, that means that the Chargers have already been in contact with the league about how to report this injury or (probably more fitting with McCoy's M.O.) to check if they had to report it and HOW it needed to be reported if so.
This also explains the re-signing of Brad Sorensen quite well. And, it sheds light on some of PR's issues in the last two games.
With just this tweet to go on, it is impossible to responsibly offer up any ideas of what the specific injury is or how long Rivers has been dealing with it. I can offer the personal observation that back issues can be excruciatingly painful, make even normal activities (like walking or sleeping) adventures in pain and discomfort, and that football is difficult enough to play well even when a player is completely healthy.
As a final word, I will offer up the fervent hope that this report is completely and utterly false and that PR is totally healthy, ready to let it rip against Niners Saturday Night.