Chelsea won the Champions League in May, but, as holders, suffered the ignominy of exiting at the group stages and tumbling into the Europa League.
Their first action in the competition comes in inauspicious surroundings at the Generali Arena, where the Blues have a point to prove and an upset to avoid.
"For them to play against the champions of Europe is massive, so we know that they will be ready," said Benitez, who was appointed interim boss after Roberto Di Matteo's dismissal following the Champions League exit.
"And the main thing for us is to be sure that we are ready, that we analyse their team properly, so we have all the reports, and we give them the same information that we would give them in a Champions League game.
"At the beginning when you saw the draw, maybe some people would have said it is not a difficult draw. Not the case. "They have been training for a month for this game. Just thinking about this game. "It is a team that is well organised and has balance. It will not be easy.
"We have to focus on Prague. Sparta are a good team, a difficult team. We have the advantage of a second leg at home - but this is an important competition."