My worse was 19 days Broken foot. fixed in few days with red packs tho..

In the begining of this season i had 7 injuries in 10 days.. After that i upgraded the grass on my stadium and the injuries droped down to.. 3 in 14 days.

Many people tend to play with a team that doesn't have good conditions/morale, they should try to keep thoes to atleast 90% or higer for any game.
Also playing a player out of his regular position increases the chance of getting injuries.