Oscar Tabarez's men start their quest for the title in Brazil against Costa Rica in Fortaleza next Saturday.
The fixture marks the first time that Uruguay and Costa Rica have faced off since 2009, when Tabarez's side won an intercontinental play-off 2-1 to secure qualification for the 2010 tournament.
Uruguay will be expected to win by a more comfortable margin at Estadio Castelao, but Muslera, who helped the South Americans reach the semi-finals in 2010, is not taking Jorge Pinto's team lightly.
"The first game is vital, though it's true to say that it's not decisive," Muslera told FIFA.com.
"Costa Rica are not the underdogs in the group. They've got players in Europe, they've really come on and they've been a tough nut for us to crack in the last few years. They almost stopped us from getting to South Africa (in 2010)."
The Galatasaray shot-stopper does not believe that Uruguay need to better their performance in South Africa and reach the tournament showpiece in Rio de Janeiro on July 13, insisting that getting past the group stages is the immediate target.
"We can't go to Brazil thinking we have to improve on that and reach the final," Muslera added.
"The fans might feel we need to kick on and become world champions, but our first objective must be getting past the group phase."
