Celtic manager Brendan Rodgers believes they can upset the odds in Valencia if they get the first goal and settle down into the Europa League tie.
The Spanish side took a huge step towards the last 16 when they won 2-0 in Glasgow last week.
Valencia have not conceded in their last three home games and only Juventus have scored more than one away goal at the Mestalla this season in the Champions League or LaLiga.
But Rodgers has told his players they must believe in themselves ahead of Thursday's second leg.
"The first goal in this game will be important," Rodgers told Celtic's official website.
"If we can get the first goal in the game, we don't need to go flying in after that. We just need to settle ourselves into the game and find our confidence.
"We know it's going to be a tough game. You can see the level that they're at and the investment, everything is there to see that they're an outstanding team.
"We have to go there with the belief and confidence that we can get a result. No matter how tough, we'll go there and if we can get the first goal it can open things up for us."
