Villa were also beaten 1-0 by Brighton in the Premier League on Sunday, with manager Unai Emery speaking about energy levels post-game.
We have to rest after a tough week," he told reporters.
Someone in the club told me last week, 'It was a fantastic week, the best week I've had at Aston Villa,' after we won in Arsenal and in the penalty shootout against Lille.
This week has been more difficult, a tough week. Now it's important to rest and recover some players, to recover some energy and go to Athens and then Villa Park trying to enjoy the moment we have in front (of us).
We're motivated, we're deserving to enjoy this moment with our supporters and our fans. Our supporters were supporting us here, but we lost.
We competed well but it wasn't enough today to get some points. Even when we were in minute 75, I was thinking maybe this draw is fantastic for us because today we are not at full energy.
The goalkeeper saved the penalty and he played fantastic today, Robin Olsen. It's not easy to be a substitute for Emi Martnez, the best goalkeeper in the world, but he's always ready to play, he's always positive, he's always respectful and always practicing ready to help the team.
Today, I was very happy with him. Even when he saved the penalty, the second action was bad luck. We tried to draw but now we're going to try and keep our advantage in the table and get the really amazing objective we have of Champions League."