Papac told the Scottish Sun: "We have to play much better in Germany because this was not enough.
"I was surprised at Motherwell's game. They played great football although they have a very young team but every game is a new story, especially in the Champions League.
"We'll start from nothing, really, and we must play at a high level. Stuttgart are a good team, maybe not the best in Europe, but they have good players and for me the Bundesliga is one of the best in Europe.
"I think Stuttgart are favourites in this game - but we must fight.
"We showed two years ago that we can play the European game.
"I expect a lot of pressure in Germany. There, many teams play more open - five or six players will try to attack you and you have to be prepared for it."