Barca will welcome Madrid to Camp Nou for the first leg of their clash on Sunday night, before visiting the Bernabeu in the return fixture on Wednesday.
Neymar's departure has opened up a spot on the left side of Barcelona's front three, and Deulofeu, who returned to the club from Everton this summer, was picked to start the Joan Gamper Trophy against Chapecoense earlier this week.
Valverde has said that he was pleased with Deulofeu's performance against Chapecoense, but the 53-year-old wants to see how the winger performs in a high-pressure situation.
"With Deulofeu, we only have his performance against Chapecoense to use as a reference," Valverde told reporters. "It's too early to judge his understanding with the other players, although I liked his performance in the Gamper Trophy. We'll see when we're faced by real difficulties."
Deulofeu, 23, re-joined Barcelona earlier this summer following spells at AC Milan and Everton.