The Blues were beaten 1-0 in Romania in the first leg of their last-16 tie.
"It was a difficult game, you could see the atmosphere and the pitch was not the best," Benitez is quoted as saying by BBC Sport.
"We are disappointed because we conceded a goal with a soft penalty and had one or two chances to score.
"Our keeper was not making any saves and we could have scored so we have to do everything at Stamford Bridge."
Chelsea travel to Manchester United in the quarter-finals of the FA Cup on Sunday.