After 2 season his passing and crossing is 17 or 18 and his creativity is only 16. I have 6 and they all are top class. This also happens to other players. You know that players can play worse if they are unhappy. I think that they also train worse too.
Some players never recover from a injury and become worse.
I have almost all the slots for scouts filled except for one. I put them on scouting trips, all scouting in England. Some of them give this particular player 5 stars while an other gives him 1. All of these scouts have judging ability and potential of 20. Different scouts have different tastes but I feel that you should buy the player that most of them give high ratings.