Vieira believes Morocco could once again spring a surprise and advance to the later stages of this FIFA World Cup.
Four years ago at the Qatar FIFA World Cup, Morocco became the first African team to reach the FIFA World Cup semi-finals, where they lost to eventual runners-up France.
Vieira stated on "The Rest Is Football" podcast: "I think the traditional powerhouses will ultimately reach the quarter-finals and semi-finals.
However, Morocco has the ability to create surprises. With a host of individually talented players, they absolutely have a chance to make it to the quarter-finals.
But besides Morocco, it will be extremely difficult for other smaller teams to make it all the way to the semi-finals."
Former England striker Gary Lineker pointed to Ecuador as a potential dark horse in the knockout stages after their impressive 2-1 victory over Germany on Thursday.
"Ecuador was unbeaten in 19 matches before the tournament," Lineker said. "Although they lost to Ivory Coast in their final group stage match, the team has a solid defense and concedes few goals, making them a very tough opponent. They might even face England later on."
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