Sell
Can we sell unwanted player cards? What to do with so many Player cards in my clubhouse ?
Forum Discussion
If the cards are untradable, you can either use them to train your other cards, or save them until the end of the season when EA finally realized people are still holding on to them.
If the cards are tradable, either you sell them on the market or exchange them. My card balance has been around 1200 or above (large majority of them are untradable) for the last few months, I agree with you that this is a nightmare.