Vale won 1-0 thanks to Ben Waine's goal and are into the quarterfinals for the first time since 1954.
Le Bris remarked afterwards: "Credit to our opponent. They played with hunger, patience, intensity. We were not at the level. It was more a second ball game, we didn't show enough to impose our strength today.
"Is what it is. It's not easy, really disappointed. Sad for our fans because they've travelled to support us and we didn't give this amount of energy to make the difference. This competition is relentless, one game 90 minutes anything can happen.
"The lads wanted to do it. We are not able to do it. It is what it is.
"The Premier League is our first objective, 100%. We tried to go strong with the players we had. We trained properly before. If you don't show enough you get punished and that's what happened today."
On pitch, Le Bris added: "The pitch is the pitch. We won't find excuses. It levels everything, technically and tactically. You put in the battle and fighting spirit and they were good at that, the crowd the stadium the event. They deserved on that part of the game to win."