The Blues host the Black Cats at Goodison Park with former Everton manager David Moyes facing a relegation battle with his current side, and Koeman knows they will be fighting for their Premier League lives.
“We need to prepare ourselves,” said the boss.
“If you’re not 100 per cent, if you take it too easy, if you are sloppy they will punish you for that. We are full of confidence but we have to show that in a good level on the pitch.
“The team and the people are happy. But in a good run you have to be prepared for what can happen. We know we are strong but it’s football and we need to keep the momentum and that starts this weekend.
“It’s always special for the players. They (Gibson and Oviedo) went to Sunderland to get more game time, that was a good choice by both players.
“They will get a respectful welcome. If they play they will do everything to win the game for Sunderland. We are friends after the game and before the game but during the 95 minutes everyone is involved in his own team.”