Gerrard has a back problem while manager Roy Hodgson has decided not to risk Torres in a third successive game following his injury problems last season.
However, both are expected to be fit for Sunday's Premier League clash with West Brom at Anfield.
Defender Daniel Agger (concussion) and Maxi Rodriguez (illness) are also missing from the squad which travels to Turkey on Wednesday morning with a 1-0 lead from the first leg.
"Steven Gerrard unfortunately has had a recurrence of the back problem which he gets from time to time," said Hodgson.
"Hopefully it won't stop him playing on Sunday.
"With Fernando Torres, we've made the decision that we don't wish to risk him three games in a row at this stage of the season with him having done so well to get back this quickly.
"Agger played in the game on Monday (the 3-0 defeat to Manchester City) which was to some extent against medical advice.
"He wanted to play but felt a bit sick after the game. That's mainly due to the concussion he suffered (against Arsenal), so it would be foolish for us to risk him.
"Maxi is sick. He's in bed at the moment with a bit of gastroenteritis, so he's out of the question."
Hodgson admits his side face a tough challenge against Trabzonspor after failing to put the match beyond reach at Anfield last week, with Joe Cole missing a penalty.
"We missed a golden opportunity to kill the game off at Anfield and now we've got it all to do," added the 62-year-old.
"It's going to be a very tough ask for the players in a difficult place.
"They are one of the two or three best teams in Turkey at the moment and Turkish football is of a very high standard.
"Everyone who's been to Trabzon tells me it's a remarkably difficult place to play.
"They're a hostile and fanatic crowd and it's a difficult pitch.
"But if we come through it we'll come through it stronger."
Joe Cole, still serving a domestic suspension, returns to the squad after missing Monday's defeat at Manchester City while Javier Mascherano has also been left out in the wake of a bid from Barcelona earlier this week.
Kick-off at the Huseyin Avni Aker Stadium is at 6.30pm BST.
Liverpool (from): Reina, Johnson, Kelly, Skrtel, Carragher, Kyrgiakos, Aurelio, Cole, Spearing, Poulsen, Lucas, Pacheco, Shelvey, Babel, Kuyt, Ngog, Eccleston, Gulacsi, Hansen.