Spurs head to France in the second leg on Thursday night having opened up a 2-1 advantage at White Hart Lane thanks to in-form Gareth Bale's brace.
Despite that lead, Friedel is wary of complacency creeping in as Andre Villas-Boas' men bid to reach the last 16.
He told the Daily Mirror: "It's two good teams both trying to progress and it's by no means a massive advantage. Just a small advantage.
"They are going to have come out and try to score and hopefully that will leave it a bit open at the back and could leave chances for us.
"I'm sure it's going to be a great second leg. The knockout stage of the competition is when these games really come alive and we're looking forward to it."
Friedel's Spurs team-mate Jan Vertonghen believes not playing at the weekend could work in the club's favour for their trip to France.
"We will be fresh for the second leg without a game at the weekend and we want to do something in Europe," said Vertonghen.
The Belgian defender believes Lyon should be wary of Welsh winger Bale, who has scored all six of Spurs' goals in their last four games.
He added: "As a winger, that's unbelievable. I'm glad I'm not playing against him."