Zenit struck twice in two minutes to win 2-0 on the night.
"There is no way the tie is over, not by a long shot. We are more than capable of getting the goals back," he said.
"I think the next goal is vitally important for us and what gives us hope is we created enough to win the game. If we get it early it can create the momentum for us."
The manager defended his decision to take off Raheem Sterling late on and send on defensive midfielder Lucas Leiva instead of pushing for what would have been a decisive away goal.
"I was just making sure we stayed in the tie, that was the important thing for us.
"As much as we wanted to go on there is another game and at 2-0 you can retrieve something, at 3-0 it would have cost us.
"The idea was to try to secure the game and keep it where it was at knowing that is retrievable and gives us a fighting chance."