Pochettino's side crashed to a 1-0 loss at Wembley on Wednesday that leaves them third in Group E
Pochettino's side crashed to a 1-0 loss at Wembley on Wednesday that leaves them third in Group E with just two games remaining.
If Tottenham lose in Monaco in their next fixture and Leverkusen beat CSKA Moscow, the north Londoners would be eliminated from the competition and Pochettino knows they will have to improve dramatically to make the knockout stages.
"Now we must win against Monaco, if not forget Champions League. That is the truth," he said.
"If we win that one, then we must win against CSKA. If not, bye bye Champions League.
"Of course we need to improve. We don't have much time. We need to lift the players because they were very disappointed. We need to look in the mirror and say 'come on we need to improve'.
"If we aren't realistic in our analysis it is difficult to improve."
After two dismal displays in their matches at Wembley, which is serving as their temporary home for European matches while White Hart Lane is redeveloped, Pochettino was asked if playing at the English national stadium had unsettled his players.
But the Tottenham manager responded by insisting the team had to take the blame for their predicament rather than look for excuses.
"We cannot blame Wembley. Wembley for me was fantastic. I enjoy coming here a lot," he said.
"We can make a lot of excuses, but tell me one place better than here to play football.
"It is where football was born. The problem is inside us. It is not Wembley.
"It is embarrassing for me and the players feel the same.
"We need to show more. We were poor again. We need to find the answer ourselves. We need to be critical of our performance. We were the problem, not Wembley. Don't blame Wembley."
Tottenham have failed to win any of their six games in all competitions since an impressive victory over Manchester City and Pochettino believes the strain of competing in both the Premier League and Champions League might be taking its toll on his players.
"We are in a bad moment. After Manchester City we don't win," he said.
"In both games at Wembley we didn't show our real quality for different reasons.
"The attitude wasn't the problem. Playing the Champions League is tough and demands a lot of mental and physical energy.
"To play the Champions League and Premier League, two of the toughest competitions in the world, it's good to analyse how we deal with that. It's maybe one of the reasons."
While Pochettino ponders how to get Tottenham back on track, Leverkusen manager Roger Schmidt was celebrating a much-needed victory that eased the pressure on him after a poor run in the Bundesliga.
"From the start we were courageous and bold. In the second half we were solid and strong in defence after we scored," he said.
"Playing here was a very special game. it was an exceptional situation. "I looked forward to it and enjoyed the fact we played well and fought hard.
"Our team showed we were together and ready to work hard."
Schmidt, whose second placed side are two points ahead of Tottenham, still expects a fight to the finish to qualify from Group E.
"Nothing is decided and I think it will go down to the last matchday," he said.
"We are in a good position now. From the start I believed we could be in the top two."