Marc Wilmots' men face the United States in the round of 16 on Tuesday and are favourites despite being without Thomas Vermaelen, Anthony Vanden Borre and possibly Vincent Kompany due to injury, while Steven Defour will miss the match through suspension.
|WORLD CUP SOCIAL HUB
|Keep up with all the latest news from Brazil and get involved in the debate on Twitter with our new World Cup Social Hub|
"I think it's clear. If we fail to qualify for the quarter-finals, it will be a failure for us because we have a great team with great players and we have the quality to reach the quarter-finals," the 25-year-old said in a press conference.
"If we don't go through, we will be very disappointed."
Attacking midfielder Eden Hazard has been criticised for his performances, with even Wilmots demanding more of the Chelsea star.
However, Witsel believes Hazard can make the difference for the Red Devils, starting with the clash against the USA in Salvador.
"We all trust in Eden. Everyone knows his great qualities," he added.
"He wants to make a difference all the time and I'm sure we will see the great Eden Hazard. He can still be decisive."