Dembele made his debut as a substitute in Barca's 5-0 hammering of Espanyol on Saturday, setting up Luis Suarez for the final goal of the match and potentially putting himself in contention to start their Champions League opener at home to Juve.
But Valverde hinted that the former Borussia Dortmund star may have to contend with a spot on the bench once again.
"You'll find out [if he will start] tomorrow," Valverde told reporters. "If I play him it's because I think he's ready.
"But he's a player, like everyone, who is training well and fitting in better each day. He could start any game.
"If he doesn't start tomorrow, he will start soon. Perhaps if he arrived earlier we'd be able to do more, but he's not had long to blend in."
One player certain to start at Camp Nou on Tuesday is Lionel Messi.
The Argentinian scored a hat-trick in Saturday's win and Valverde feels safe in the knowledge that an in-form Messi makes Barca that much stronger.
"It doesn't necessarily calm me [having an in-form Messi], but to see Messi playing well certainly makes us a better team.
"It's very important for this game for him to be feeling confident. Let's see how it goes."
Paulo Dybala is another who comes into the match in fine form, with the Juve striker scoring five times in three Serie A matches so far this season, but Valverde insists Barca will not be concentrating solely on the former Palermo star, who scored twice at Camp Nou in last season's quarter-finals.
"He's an important player in his team and in the world," Valverede said. "We're sure of that, but no more than [Gonzalo] Higuain or other players.
"Juve are a unit and play consistently well as a team. They have individuals, but it's the team which concerns me the most. They look good, I watch the Italian league.
"They look strong and ready for the season. You could say they've lost or gained a player, but those are the kind of comments people make about every team in every country."