Benitez's men have endured a difficult start to the campaign - bowing out of the Champions League in qualification while also losing 1-0 at home Chievo in Serie A on Sunday.
Those results have led to criticism in certain quarters, with Benitez calling on players and fans to work together ahead of the visit of the Czech champions.
The Spaniard feels Sparta will play with freedom at the Stadio San Paolo and warned of the threat they can pose, having taken them on while in charge at Chelsea.
"Results are important but data from the last three months has been fantastic. Now I read with great surprise that it is the worst start in four years, but I did not read any positive news after the first win," Benitez said on Wednesday.
"We must be united, the fans have understood this and have helped the team. We are all sorry, but so many people have realised that it is important for us. Now we are focused on Sparta Prague, the best team in their championship.
"Against us they have nothing to lose, we have prepared for the game well and we will have to work together in order to win tomorrow.
"I played against Sparta with Chelsea and it was two difficult games. We must move forward, but we are thinking about the game tomorrow.
"We have to play to our best in this competition, we have to win tomorrow and look forward. I have experience in this, we have to have a good group stage. After that, anything can happen."
Benitez also hinted at making changes to his starting XI, with Michu potentially coming in for their Group I opener.
"When I arrived at Valencia and starting making team rotations they said there that I was crazy, but I won La Liga and the Europa League," he added.
"I can make the team rotations if we have an adequate squad, whilst the changes are only right in the case that we win. We will see what happens tomorrow."
