Spurs will need to overturn a 4-0 deficit in the second leg at White Hart Lane after going down to goals from former Arsenal striker Emmanuel Adebayor (two), Angel Di Maria and Cristiano Ronaldo in the Spanish capital.
Asked about his side's chances of making it through to the last four, Redknapp said: "Well, it's going to be very difficult. It certainly couldn't be much more difficult than being 4-0 down to Real Madrid, but we're at home, we'll give it a go.
"It's never over until it's over and you never know, though obviously we've got a mountain to climb, there's no doubt about that."
Source: PA
Source: PA