Injuries and Physical Condition % are directly related.
Physical Condition % reduces by 2% each League match played and is replenished by 10% for every League game he does not play. If a player sustains an injury, it will cause a significant reduction in Physical Condition % - somewhere between 10% and 25% depending upon the medical staff you have employed.
In Footy Boss, we don't believe in restricting your use of players if they are injured. Just like in any real football match, players are often required to play with minor injuries for important games. That said, any player that does play injured has a far greater risk of doing further damage which means further reduction to their Physical Condition %.
Physical Condition % as displayed for each player, directly affects the players skills. For example, if your player has a total of 100 skill points and a Physical Condition % of 90%, he will in essence have total skill points of 90 for the next game he plays (90% of 100 = 90).
Not only does a player's skill reduce as the Physical Condition % reduces, it also increases the risk that the player will be injured in their next game. Injury will result in significant Physical Condition % penalties (between 10% and 25%).
Once again, we do not stop you from playing this person however, given the resultant skill reduction and increased risk of further injury, it is generally wise to rest a player to get their Physical Condition % back to a reasonable level before sending them back onto the field.
NOTE: If your team is on their way to a blowout victory in any League game (up by 80+ points at any stage), your players Physical Condition % will only reduce by 1% instead of the usual 2% given the lack of intensity required to win that game.