Napoli coach Rafa Benitez says Sparta Prague could make life difficult for his team.
The Czechs were very disappointing last week against FC Teplice away from home but the Spaniard warned his players not to underestimate the quality of Vítezslav Lavicka's men.
"I know Sparta Prague, they are the strongest team in their country and they are used to feature in Europe," Benitez said ahead of Thursday's match.
"I faced them when at Chelsea and we won after two hard-fought matches.
"They are solid and good at set-pieces, we have to give our best to start the competition with a home win."
The Partenopei kick-off their European campaign after a shock home defeat against Chievo on Sunday but the Spaniard is not worried about the confidence of his players.
"We know what our strengths are," added Benitez
"We fought hard to win our first game against Genoa and lost against Chievo after having 33 shots at goal. Yet it seems there's a dark cloud hovering over our heads, which is not the case.
"We will go far if we play the way we did in the first half last Sunday.
"We can improve, we have to be good in controlling games, we can't go out there thinking we can win all games in the first half of the game.
"We need to be patient and read the game properly."
