The Catalan giants have only won one of their last four games and appear to be lacking the usual clinical edge that they so famously possess, but Messi thinks they can regain their best form in time for Tuesday.
The dip in form has seen Barcelona lose two El Clasicos as well as an all-important Champions League tie, however, Messi thinks it would be silly to write the Primera Liga leaders off just yet.
"It is obvious that we have to do a little more. Lately we have come from a run of defeats and we are aware of what we need to do to change that," said the 25-year-old.
"There is a key game coming up for us to react and change things.
"To come back is what we all want. We know it will be very difficult, but we believe it's possible. If they can do it there, we can do it here.
"We know that if they score a goal it will be more difficult and that Milan have very good players, but we will have our chances."
Barcelona are still without manager Tito Vilanova, who is undergoing treatment for cancer, however the Argentinian forward is refusing to use that as an excuse.
"It has affected us a lot and I think it has taken its toll when it comes to preparing for each competition, but we have a strong dressing room and I don't think we can put the blame on this situation," added Messi.
Argentina's captain also was quick to acknowledge the impressive form of domestic rivals Real Madrid as he watched them advance to the quarter finals of the Champions League after beating Manchester United 3-2 on aggregate.
"Madrid are demonstrating that they are very strong. They knocked us out of the Cup and they are now in the quarters of the Champions League.
"They are a candidate to win the Champions League, just as United were."