David Unsworth said the way Everton conceded three late goals to suffer a 5-1 defeat against Atalanta was "not acceptable”.
Sandro Ramirez’s first goal for the Club got the Blues back in the game at 2-1 with 19 minutes remaining but Robin Gosens’ volley and a brace from Andreas Cornelius saw the contest end in a comfortable win for the Italians.
Everton, who already knew they could not progress from Europa League Group E, had earlier trailed to two Bryan Cristante efforts either side of the break, while Joel Robles saved Alejandro Gomez's penalty early in the second half at 1-0.
“It was disappointing to get a foothold back in the game and get the crowd on our side at 2-1 with a great finish from Sandro, but to concede the way we did and in the schoolboy manner we did was just not acceptable and the players know that wasn’t acceptable,” said Unsworth.
“I thought the start was okay but, as is the story of our season, we gave away a cheap goal out of nothing.
“Then we changed things around, we got back in the game and that’s something we’ve spoken about in the weeks that I’ve been in charge; to play on the front foot.
“It takes a special type of player to have the guts to get on the ball at Goodison Park. There was no pressure on the game tonight and it was an opportunity for players who haven’t been playing to stake a claim. But when we concede and lose the game in the manner we did, they can’t complain when they’re not in the team.”
Everton now travel to Southampton on Sunday looking to build on the victory over Watford and last weekend’s point at Crystal Palace.
The Blues can move above Mauricio Pellegrino’s side with a victory and Unsworth added: “I don’t like dismissing getting beat. I don’t like getting beat - you should never like it - so we’re going to have to speak about it.
“But very quickly we’re going to have to speak about Southampton on Sunday. There’s a lot of players to come back into the fold and we’ll pick a team to go and do a job.”