Koeman has sought to exonerate his players for their below-par performance, instead suggesting that he had not prepared his charges properly.
The Dutchman told BT Sport: "This is not the time or place to criticise players, I need to criticise myself because the team was not prepared for this tonight.
"We saw the clips of Gomez beforehand. That's the individual quality of one player but the whole team of Atalanta was better prepared than we were today.
"We knew from the beginning of July the start of the season is really tough. Okay we need to expect it, but that's not the problem – the problem is what we showed in the first half."
Everton return to Premier League action this Sunday as they travel to top-of-the-table Manchester United. body check tags ::