Emile Smith Rowe had Fulham ahead before Wout Faes' equaliser for the Foxes. Alex Iwobi struck Fulham's winner after halftime.
"When you lose a game, you should be disappointed," Cooper said at full-time. "You’re never going to accept losing too easily – and that’s how I feel, that’s how the guys feel. I’m sure the supporters are the same.
"Fulham definitely started the game better than us, which can often happen in a game away from home, but I felt like we gradually got to grips with the game.
"I know we went 1-0 down, but we got to grips with the game, we showed a bit of momentum. We had some good attacks, some dangerous attacks, some territory. We won some set-pieces and scored off one of them.
"It’s ridiculous to think that it could have been disallowed. At half-time, we were really confident that we could go and win the game to be honest – or certainly get something from it.
"I thought you saw that in the first phase of the second half. I thought we got into some dangerous positions.
"I would have liked us to have made more of it, in terms of more attempts on goal, and hopefully that will come as we integrate new players and players get stronger. We’ve been punished, on both goals, for that moment where you’re not quite right tactically in the game."