Just found an interesting article on the internet regarding the frequecies of injury in football:
http://bjsportmed.com/content/33/3/196.full.pdf
27.7 injuries per 1000 hours of activity happen during competition, 3.5 injuries per 1000 hours of activity happen during training.
Therefore based on the statistics on this article, A manager in top eleven should experience on average 23.5 injuries for a 52 match season (26 League, 13 Champions League, 13 Cup games)
One of each training on normal, would be 100 mins per player per day, for a 20 man squad over a season its 56,000 minutes of training and that would leave an average of 3.25 injuries per season.
We would looking at an average of 25-30 injuries per season on a normal regime.