Sparta have not lost at home in Europe in their last 11 matches, a run that stretches back to 2010-11.
Vaclik is confident that they can continue that run on Thursday, but believes that his side will have to be at their best if they are to beat Chelsea over two legs.
"I believe we will add one more match to that run and travel to London with a result that keeps our chances alive," Vaclik told UEFA's official website.
"To succeed, we'll have to play our best football. Even if Chelsea are not having their best period right now, they have the winning mentality of a big club and self-confidence."
The match will be Sparta Prague's first competitive fixture since December 6.