After 2 days of general slowness (not talking about servers...), we finally arrived to the beginning... what Newton07 said was right.
Doctors help prevent player injuries, and help injured players recover more quickly.
we added in doctors skill into the formula which determines how severe the injury is (including the chance that the injury doesn't translate into an injury which lasts longer than the game).This is equivalent to keeping the length of the injuries the same and speeding the healing process proportional to the doctors skill.
I keep the same doctor all this seasons so i think the problem should not be there...