Deco has played down Barcelona's favourites tag ahead of Wednesday's Champions League final with Arsenal.
Deco insists Barca must be at their best to beat Arsenal
The midfielder is the only member of Barca's squad to have won the European Cup - he helped Porto to glory in 2004.
However, he said: "We can't say we are the better team. Even if we were it wouldn't guarantee us victory.
"If you don't respect your opponents things can start going wrong. We need to be serious and fully concentrated so that we don't make any errors."
Deco insists that his side will not be taking the Gunners lightly and added: "AC Milan were winning 3-0 last year against Liverpool and ended up losing in the end.
"We need to be serious, calm and fully concentrated so that we don't make any errors."
Deco was also upbeat after news that Argentina striker Lionel Messi has been included in Barcelona's 22-man squad, despite not having played for more than two months.
Messi tore a thigh muscle during the second leg of the knock-out tie against Chelsea on 7 March.
The 18-year-old trained with the team on Monday but coach Frank Rijkaard will leave it late before deciding if he will select him.
"The fact that Messi will be with us will make us stronger but we don't know if he will play in the final," said Deco.