The Czech Republic side earned a superb 1-1 draw away to Inter in their opening Group F game before succumbing to a 2-0 home defeat against Borussia Dortmund.
🔊 Valverde: “@slavia_eng are an opponent who will go all out, we expect to see a great team like the one that showed up in previous matches. Tomorrow, the three points are very important.” #SlaviaBarça pic.twitter.com/ZPeQkoIeQ1— FC Barcelona (@FCBarcelona) October 22, 2019
They now face LaLiga champions Barca twice in the space of a fortnight, with few expecting them to cause an upset against their more illustrious rivals.
Valverde has seen enough from Jindrich Trpisovsky's side to suggest they could cause problems for his outfit, though.
"We are looking forward to a game against a great rival, which has already demonstrated its strength in two Champions League games this season," he told a media conference.
"They do not turn their back and they approach games with many players in attack. They run a lot and the game is a fundamental one for both of us.
"They are a dangerous team. They are a great team and you could see that in the Inter game. They played with personality and dominated the game.
"People may think that we are favourites, but it is an 11 against 11 game. They are a tough team and we will have to work hard."
Barca overcame Eibar 3-0 in LaLiga at the weekend, with Antoine Griezmann, Lionel Messi and Luis Suarez all on target.
Valverde would not be drawn on whether the trio would start against Slavia but believes their understanding will only get the better the more they play alongside each other.
"I see the players talking, like everyone else," he added. "It's about understanding and that is achieved by playing together. The great players understand each other quickly."
Barca are second in Group F with four points from two games, behind Borussia Dortmund on goal difference.
They are without the injured Samuel Umtiti, Sergi Roberto, Carles Alena and Carles Perez for the trip to the Czech capital.