Former Spurs goalkeeper wants to see an improvement in the return leg.
Dortmund won 3-0 with Pierre-Emerick Aubameyang and Marco Reus (2) scoring the goals.
Spurs were already without the suspended Dele Alli and Eric Dier and Danny Rose through injuries, before Mauricio Pochettino made a further five unforced changes to the team which started the North London derby, with top scorer Harry Kane on the bench.
Former Tottenham goalkeeper Ray Clemence gave his verdict after the game, using Twitter to express his sadness at the result.
For Spurs to turn it around will require a humongous effort in the second leg, and hope Dortmund are caught off guard and complacent, but it would take a hugely optimistic view to consider that Tottenham can still qualify for the quarter-finals.
The squad will hope to bounce back at the weekend when they face strugglers Aston Villa in the Premier League.