The £135m summer signing from Borussia Dortmund was given a 20-minute runout in Thursday's Copa del Rey last-16 tie, 110 days after last featuring for his new side.
Dembele picked up a hamstring injury on his first La Liga start for the Catalan giants and has been made to wait for his comeback, which came at Balaidos in the 1-1 first-leg draw.
Rather than stick the Frenchman out wide, though, Valverde instead played him in the role usually associated with the rested Luis Suarez.
"It was so that he could play in a position where he was released of defensive obligations, which were a bit stressful at that time of the match," Valverde told reporters.
"When we know that this was the first game of this player after almost four months without playing, I preferred that he be in a position where he can gradually get used to the game.
"We must take into account that the pace of a whole match against a first division team. For Ousmane, it would have been excessive."
Dembele is now in contention to feature in Barca's home league match against Levante on Sunday afternoon.