You have to -don't see the stars and see what they do- as Ive said in another thread I'm very practic now with that, so, if don't work, sell.
Too I have to say like eeverywhere that you don't need a full team, 1 new player per line and season is fair enough, so if you see that the team fail don't waste greens training players of 5* to 7* if they don't work because probably many times you don't will have expected results.

See, prove, test, decido who's the worst, and buy anoher player for thsi position. As I always say, a page with the stats of the full team will help us to see what r your players doing (and the Quality page too).
Maybe they spend the live matches drinking fresh beer