Everton prepare to square off against Norwich in the third round of the league cup on Tuesday and it is widely expected that manager Koeman will look to give a number of unused Toffees a chance to impress on the night.
Koeman has now talked up the importance of the clash for the fringe players who are struggling to earn regular first team football and has urged them not to miss out an opportunity to impress during the encounter.
The Dutchman said: "It is always an opportunity for players who did not play in the last few weeks.
"Some players will get their chance and you take notes about that. After tomorrow, you make your conclusion about players and competition.
"It is a big opportunity for some and they need to respond. If they don't play well, then it will be difficult."