Serbia coach Dragan Stojkovic said Wednesday his side could learn from their narrow 1-0 loss to England before Thursday's crunch Slovenia game, having shown England "too much respect".
England dominated the first half taking the lead through a Jude Bellingham header after 13 minutes. Serbia however fought back into the game after half-time, forcing England to fight hard and hold on to claim all three points.
"Against England we started playing with too much respect for them, like they came from another planet," the coach said.
"It should not be like that. We've played better against them later in the match and that's how we'll play against Slovenia."
Denmark's 1-1 draw with Slovenia in the other Group C fixture means Serbia can take a huge step towards reaching the knockouts with a win on Thursday in Munich.
A loss or a draw in that match would however represent a significant setback for the Serbs in their first European Championships as an independent country.
Asked if he was an optimist, Stojkovic said: "Why wouldn't I be? We believe in our team and in our football.
"We're going to do everything we can do to win against Slovenia.
"We have to win, we have to win every single match. And then the vikings will come from the north, the Danes, and we'll have to beat them."
The colourful coach said he was in a bad mood, complaining about having to scan his accreditation "all the time, every time I go through any kind of door."
"It's like I'm entering a NASA space station, not a stadium.
"That's why I'm not smiling."
Serbia striker Aleksandar Mitrovic drew a blank in the opener and called on his side to attack.
"Tomorrow I want to stand as close to the goal as possible," said the Al Hilal forward.
"Things can change very rapidly in football, but if you ask me I'd like to attack as much as we can -- I want to have the ball for 90 minutes and be constantly on the attack."
Stojkovic said he expected a good-natured encounter between the two sides, calling it "a real football atmosphere".
"Lot's of Slovenians, lots of Serbs. Whoever wins will buy the beers after that."
dwi/bsp