No, I didn't use "Enter" key and, as someone else noticed, there is no "Enter" or "Invio" button.
Besides all, I did this operation after the end of my team's game (about 19.00 here in Italy, more or less..)
Meanwhile the auction for the same player finishes almost two hours earlier (about 17.00 italian time...)
If I really fired my player, in a way or another, is it possible to see him on auction a second after ? with a delay of 2 hours ?