Sparta host Chelsea, last season's Champions League winners, in the first leg of the Europa League last-32 in their first competitive fixture since December 6.
The hosts are confident though, having last lost at their Letna Stadium home against MSK Zilina in the 2010/11 Europa League play-offs, while Chelsea have one win in five matches.
"I believe we will add one more match to that run and travel to London with a result that keeps our chances alive," Vaclik said on www.uefa.com.
"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."