He said: "It's knockout football now without a doubt". "We've got to win and win the next one after that". But we have to beat the Slovakians first.
"But we have to win so I've got to pick the best team, even if some of them might be a bit exhausted they might have to play a smaller part in the game and think about what goes on in the last half hour of the game".
Victories for Spain - who thrashed Macedonia 5-0 in Gdynia thanks to a hat-trick from Real Madrid's Marco Asensio - and Portugal in their opening games on Saturday mean that they already hold a significant advantage in the race for the best runners-up spot, meaning England's progress to the last four is likely to depend on them winning the group.
England U21 captain James Ward-Prowse says senior team manager Gareth Southgate has been offering advice to the team.
That leaves England desperately needing a win here before they face hosts Poland on Thursday.
"He's been around and spoken to us, pulled us aside individually and seen how we are, and it's great to have him and Steve (Holland, assistant) around, " said the Southampton man.
"We want to make sure that we're not having those same feelings again.it's not a nice feeling when you don't reach the level that you should do". It was great to see him here.
He said: "It is one of those things and it is a decision from the club that has been made".
"I went away and in the long run it was a very good thing to happen to me". Although I didn't play in any more of that tournament it was a wake-up call.
"We didn't play anywhere near as well as we can [against Sweden]. The club and the players have shown that we can cope with managers and players going".