The Frenchman replaced Philippe Coutinho in the 70th minute, with the score 2-1 in Barcelona's favour, and he went on to score the fifth in a 5-1 victory, though it came at a cost as Dembele will now miss three to four weeks with a hamstring strain.
"He had some annoyance the day before, but I decided to risk him because it was such a decisive match," Valverde said about Dembele in his press conference.
"And, according to the scoreline, I decided to bring him on, although he will now be out for three or four weeks.
"The feelings that I had before the game was great; he thought he could play without any issues and wanted to start.
"If it wasn't for the scoreline, I wouldn't have put him on."