Oihan Sancet's penalty was sandwiched by Barcelona goals for Lamine Yamal and Robert Lewadowski.
"The game was open in the first half. We had chances and so did they," Valverde said post-match.
"Barcelona started the second half strongly and we didn't respond well. That's what we have to take from this match. It was difficult, we tried to recover, but then they scored and that was a big blow for us."
“We're doing well. When you come to play against an opponent like Barça, who are candidates to win any title, it's normal that we'll have to suffer and work hard.
"The match against Getafe was different. This is a daily battle in which we always have to fight to win. Today we didn't manage it, it was tough, but we really gave it a go.
"It's true we still haven't won yet and now we're in a slightly more difficult position against Valencia. But it's another chance to get three points.
"We always give our best and we'll do so on Wednesday."