Spurs must turn around a 3-2 first-leg deficit at White Hart Lane if they are to reach the lucrative group stage for the first time.
Manager Redknapp was confident they would do so but said: "Listen, if we can't win Wednesday, then we don't deserve to be in the competition. If we can't win Wednesday, what chance have we got anyway? So, we find out how good we are Wednesday."
Tottenham had been expected to roll over Young Boys in last week's first leg in Bern.
But a shocking first half-hour on the Swiss runners-up's plastic pitch saw the visitors forced to fight back from 3-0 down.
So horrendous was their defending, Redknapp confessed he feared they might have fallen as far as 6-0 behind.
And he urged his side to mirror the kind of fast start their opponents inflicted on them last Tuesday.
"We've got to swarm all over them if we can," said Redknapp, who also wants the home fans to create an "intimidating" atmosphere.
"I wouldn't sit here saying we've got to be patient. I think we've got to get after them."
He added: "If the players play as they can play, we're going to be very difficult to beat."
Source: PA
Source: PA