As a selling option in FUT 20, you are able to discard or fast sell your items and cards to the FUT system for a lower price. This feature is called "Quick Sell" or Discard Option.
By applying quick sell option to an item or card in FUT, that item/card will be gone forever and you will receive an amount of FIFA coins based on your sold card type and value. Below is the price list of quick sell option in FIFA 20 Ultimate Team including the item types:
FIFA 20 Quick Sell prices above are shown in number of coins. You will get these amounts after applying the quicksell option to your item. You need to confirm your sale after pressing Quick Sell button and once you confirm it, an undo action will not be available.
There is a quick sell calculator tool available online which allows you to calculate the price of quick sell option based on your item value.