Messi was one of a number of Barcelona stars who were far from their best as Bayern ran out a 4-0 winner at the Allianz Arena but Muller believes the Argentina ace will provide a far sterner test in the second-leg clash on Wednesday.
"Barca away at Camp Nou - that's a completely different proposition altogether," Muller told a press conference on Tuesday. "They will come forward at us a lot more than in the first leg, they’ll have more shots on our goal and more possession, which is their strength. I think we’ll see a different Messi in this game."
He added, "Everyone knows that he is the core of their team. If you score 50 goals every season, then it’s clear that the team will depend on you. I don’t really know what his situation was in the first game in terms of fitness, but he came off the bench at the weekend and scored a great goal.
"I think we’ll be much busier with him in this game."
Teammate Bastian Schweinsteiger added that the Bavarians must be careful not to rest on their laurels following their first leg triumph and insists they will attempt to score a crucial away goal at Camp Nou.
"We opened the door to the final with the first leg result," Schweinsteiger said, "but we haven’t got the job done yet. We still need to show a lot of passion to make sure we can go through, especially against a team like Barca.
"I think we have a great team compared to last season and all the players are fit for the match. That explains why we are where we are. It'll be tough because Barcelona are capable of doing great things, we know that. We have played very well in this season's Champions League. If we score one or two goals we know it'll be even tougher for Barcelona. If we have the chance to attack, we will."
Schweinsteiger is one of a number of Bayern stars who face being suspended from the final should they pick up a yellow card on Wednesday, but the Germany midfielder has stressed the team's sole focus is on doing what they must to reach the final at Wembley.
"We are all dreaming of getting to the final. There may be difficult moments in the game and we know the risks. If someone gets another yellow card, then that’s unfortunate. But our focus is doing what we can to make sure we get to London."
Follow GOAL.COM on