The Blaugrana were held to a draw when the two sides met at Camp Nou in the group stages before battling their way to a 3-2 victory in the return fixture in Italy.
Valdes is expecting another difficult encounter with the Italian champions, even though confidence within the Catalan camp is sky high in light of a nine-game winning streak in all competitions.
"Milan are always a very dangerous team," the goalkeeper told reporters on Monday. "We saw that in the group stage.
"They are a great team with great history. A tie against Milan, who are one of the biggest sides in Europe, will be difficult.
"But it is coming at a good time for us and it is vital that we try to play our usual game."
Barca's winning run has seen them close to within six points of Primera Division leaders Real Madrid. However, Valdes insists that the players are not getting carried away by the talk that the title race is now suddenly back on.
"When we were 10 points behind we did not change our approach, and now that we're six behind, we will not do so either," the Spain international explained.
"We have to compete against each and every opponent and just try to collect the three points.
"The press has been saying that the league was impossible for us but the message has always been the same on our part: never give up.
"However, the six-point gap is still substantial. Only time and the games will decide if the deficit is reduced. We have no choice but to win every game and wait to see what happens."
Barcelona tackle Milan at San Siro on Wednesday before hosting Athletic Bilbao at Camp Nou at the weekend.
Between November and February, Goal.com published 10 exclusive extracts from Graham Hunter's highly anticipated new book, 'Barca: The Making of the Greatest Team in the World'. Click here to read all 10 extracts. Don't miss it!