Everton take on Italian Serie A side Atalanta in the Mapei Stadium in Reggio-Emilia later on today and Koeman says they are taking neither the competition or the opposition lightly.
Everton have travelled with a strong squad, and although there could be changes from the side that lost against Spurs at Goodison Park, there will not be too many.
“I am the manager and I take this competition really seriously," Koeman said. "We won our qualifiers. We can show it won’t be different tomorrow. We have more players available.
“You can make some rotation, but we start with a strong team. After last weekend we need to react.”
Koeman is still smarting from that defeat against Spurs and added: “If you lose the game, you get another opportunity to put it right. So I am confident about tomorrow."