My GK has lost the plot and is quite often getting performances below 3 in games.

Is there any way to improve a players form? If not, is this something that could be added to the game in some way, even if it means introducing manual training into the game?

It could be related to the new way we calculate the match rating, which is based solely on number of defenses and goals conceded. It’s easy to adjust the calculation now if it proves to be too harsh with the goalkeepers. There is no such concept of player form at the moment, but it’s a nice future improvement to have along with training.