Barça made an almost faultless start to the season only dropping points in the league before Christmas with a 2-2 draw with Real Madrid at the Camp Nou, while they also lost against Celtic in the group stage of the Champions League.
But now signs of tiredness are beginning to set in.
"Against Madrid we will have to produce our best football as we will be against a great rival. We need to be at our best in order to get into the final," said Messi, ahead of the semi-final showdown in the Catalan capital with the scores 1-1 from the first leg at the Bernabeu.
The teams then go head-to-head again in the league at the weekend but with Madrid trailing Barça by 16 points in the table there is little more than pride at stake.
While they were expected to roll over AC Milan last week in the Champions League in typical fashion, in the end they were unable to break down a well-organized but not remarkable defence as they lacked the movement and the speed of passing.
Even four-times world player of the year Messi was largely anonymous as they had plenty of possession but were well contained.
At the back their defence was opened up on the rare occasions that Milan attacked and they got two goals to give them a significant advantage ahead of the return leg.
Barça were again lacking potency in attack in the first half against Sevilla at the weekend and went behind before turning the game around in the second half with goals from David Villa and Messi.
The Argentine continued his record scoring run in the league to 15 straight games and will be looking to add to his tally against Madrid but there is also plenty of concern about their leaky defence.
"We need to get back to playing how we were doing before and not think about what happened in Milan or the Sevilla game.
"We took on Sevilla on the back of a bad result and that was noticeable but we got ourselves going in the end. It is difficult for us not be distracted by Milan and although we didn't play well then we shouldn't allow it to get to us," said Messi.
"The cup and the Champions League are down to us and we aren't concentrating on the opposition. Physically the team is in good shape and I am used to playing in all the games," he added.
For Madrid it is the first of two make or break games with the other coming in the Champions League against Manchester United.
They struggled once again away to Deportivo la Coruña at the weekend with a weakened side and Cristiano Ronaldo was among those brought on in the second half to turn the game around and give them a 2-1 win.