The Germans must overturn a 1-0 deficit from the first leg as they seek a third quarter-final appearance in the competition in a decade but were already without talismanic attacking midfielder Marco Reus ands Mario Goetze.
"Guerreiro is doubtful for tomorrow. He has a stiff thigh muscle from the 6-2 win over Bayer Leverkusen (on Saturday)," Tuchel told reporters. "We will take as decision on this tomorrow."
Despite the absences, Tuchel is confident Dortmund had the quality and spirit to overturn the deficit.
"We are in a position to beat Benfica. We took that from the first leg with us even though the result was a paradox. We feel fully prepared and should we succeed it would be a major boost for us," he said.
"Tomorrow we have a floodlight game and it's all about scoring goals and going forward."
Dortmund wasted a bagful of chances in the first leg in Lisbon and had a penalty saved before Benfica snatched victory with a Kostas Mitroglou goal.
But they have recovered, scoring 12 goals in three straight league wins since.
Bundesliga leading scorer Pierre-Emerick Aubameyang, who squandered most of those chances in Lisbon as well as the spot- kick, has also rediscovered his scoring form, netting twice against Leverkusen.
"I'm very happy that Aubameyang has scored again," Tuchel said. "Tomorrow would be the best day to carry on that form."
(Reporting by Karolos Grohmann, editing by Ed Osmond)
