"The performance in Barcelona was good, but we can play a lot better," said the Reds' boss.
"The only thing about Wednesday we couldn't improve was the final result, but as a team I know we can do even more. I don't just say this for effect. There were parts of our game we could have done better.
"Of course we did a lot of good things, especially in the second half. To win in the Nou Camp in front of 100,000 fans is really good and when I saw the pictures of Bellamy and Riise smiling together at the end I was really happy. But we must continue to think about where we can improve and focus on Sheffield United. I have told the players to forget about Barcelona now.
"We know Sheffield will be a tough game. They have shown this with their results and have had a lot of time to prepare for this game.
"When you come back from a European game it can be a dangerous time. Players can be more tired or lose focus easier."