While Hearts were busy putting six goals past Inverness Caley Thistle in the Premier Sports Cup last weekend, Rapid went two better.
The Austrian Bundesliga leaders warmed up for Thursday's first leg at Tynecastle with an 8-0 demolition of Grazer AK.
Danish striker Tonni Adamsen scored four of the goals, with Ercan Kara grabbing an early double at the Allianz Stadium.
Rapid finished fifth in Austria's top flight last season, but have scored 29 goals already this term, winning all eight of their competitive games.
Adamsen already has six goals to his name, while Ercan Kara and Moulaye Haidara have five each.
Former Celtic winger Marco Tilio signed for Rapid in August last year and is likely to feature against Hearts.
Hearts have already been stung by Austrian opposition this season, but Vrancken expects Rapid to be better than Sturm Graz in certain areas.
"Rapid are a good team," Vrancken said.
"When you compare them with Sturm Graz, then they want to also press high, they have a strong pressure style. Sturm were more direct and played from second balls, fighting for those balls.
"Rapid have the physicality, but they also have the quality to play. I think on the ball they are better, or different, let's say, better in combinations. Always when you play in Europe, especially when you're on the unseeded side, you always draw good teams, so we have to be top level."