So you still have 2 stars in training? One of the following might be happening:

1. Your coaches are not very good, meaning that they can not train your players very well. Very important are the training outfield players and working with youngsters attributes.
2. Some specific player is beginning to show signs of age, resulting in his stats dropping.
   

   The ages at which players reach their peak are

   Goalkeepers	31-32
   Defenders	30-31
   Midfielders	30
   Attackers	27-28

   However it takes at least a couple of years before you start seeing reds,and this greatly depends on each player's work rate and determination.

3. Some player might be unhappy with the conditions in the team in general, or he might be unhappy with the training schedule! It is very important that you click on the star rating of the player and see what your coaches say: If they say that the training schedule is a bit too intensive for this player's morale, then you might consider using an alternative.
4. It is also true that a training schedule's success depends on each player's motivation and professionalism. Some players will perform well for the same schedule, with which others might fail. So you should try to personalise each training schedule.
5. The coaches are very important for your training. A coach with low motivation and man managerment stats is more likely to fail in urging lazy players to train harder
6. A player might be coming from a long injury! His stats might be in red, but he will soon recover when he restarts training!