The Blues travel to the Czech capital for their first away fixture in Europe since Roberto Di Matteo was sacked following their exit from the Champions League group stages.
"This is a massive city, massive club and a massive competition," Benitez said.
"We are really pleased to be here. Obviously, you cannot change things. The Champions League is a massive competition, but the Europa League is also a massive competition.
"We play against an historic team. We're really pleased and, for me, I try to give my players the right message. We know it will be tough."
Benitez won the previously-named UEFA Cup with Valencia in 2004 but he is unsure whether success in the tournament with Chelsea will see his contract extended beyond the end of the season.
"We have to concentrate on the future and the future is tomorrow," said Benitez, whose position could yet be under threat with four wins in 11 games.
"I cannot talk about what will happen in three months' time. We have to concentrate on this competition - it's quite difficult - and tomorrow will be a tough game, so that is my priority."