Benfica face the toughest possible prospect in the Champions League - getting a positive result at the Camp Nou against Barcelona.
The Portuguese side will be assured of progress into the next round with a win over Barca, who have already qualified from Group G as winners.
Benfica and Celtic are equal on seven points, with the Scottish champions, who play Spartak Moscow, needing to better the Portuguse's team's result to go through.
"We have worked (on things) thinking we wouldn't have Carlos Martins or Enzo Perez," Benfica manager Jorge Jesus told reporters. "We have worked on various alternatives. We know our midfield is weaker than normal, but we will decide who to field, be it Andre Gomes or Andre Almeida.
"Predictions for Celtic vs Spartak are no use -- I don't want my players to think about that. If we have good news at the end of the match, then all the better.
"We have to improve our performance compared with the match against Barcelona in Lisbon. Tomorrow we need the same strategy we used in the first half. We can't make the same mistakes twice, for example not putting pressure on Barcelona.
"We believe in what we do, we believe we are brave and we believe we are facing the best team in the world, along with Real Madrid. We believe we will be lucky for this match and we believe we can surprise Barcelona."
Barcelona manager Tito Vilanova might rest some of his senior players, although Lionel Messi is expected to start as he closes in on Gerd Muller's record for most goals scored in a calendar year.
Messi is one short of the 85-goal mark, and will look to equal or even break the record against Benfica.
"Gerd Müller's record of 85 goals in a calendar year isn't an objective -- we have to take it in our stride," Vilanova said. "We all know Lionel Messi is about to reach that record, but it's just part of his game.
"Leo will probably set a new record, but the important thing is the match, not other things. Messi is the same as usual -- he's in good form, eager to play. He isn't any different at all. He's used to playing under the pressure of being close to a record."
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Expected lineups: Barcelona: Valdes; Montoya, Pique, Puyol, Adriano; Busquets, Iniesta, Fabregas; Pedro, Villa, Messi.
Benfica: Artur; Pereira, Luisao, Garay, Melgarejo; Salvio, Matic, Gaitan, Perez; Lima, Cardozo.
Prediction: 3-0 to Barcelona
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