Germany remain the top-ranked side in the world having lifted the World Cup for the fourth time in 2014.
England have not reached the quarter-finals of a World Cup since 2006 and were stunningly beaten by Iceland in the knockout stages of Euro 2016.
However, they went through qualifying unbeaten and held Germany to a 0-0 draw at Wembley on Friday.
Belgium, quarter-finalists at the last World Cup and European Championship, were similarly dominant in qualifying, dropping just two points.
Asked if Germany could defend the title, Voller - who won the World Cup as a player in 1990 and took them to the final in 2002 as a manager - replied: "Yes, of course. It'll be complicated, because except Brazil no one ever defended the title, maybe before the war Italy did, too, but only five teams participated back then.
"Generally speaking, it's very difficult, but four years ago before the World Cup in Brazil, no European team had ever won a World Cup title in South America.
"Our guys are definitely the big favourites, maybe with Spain and France, maybe England, who have a very good team, Belgium, but from the quarter-finals onwards, sometimes what's decisive is the daily form and then you'll see. But the possibility is a given, that's for sure."
Voller is sporting director at Bayer Leverkusen and is confident winger Julian Brandt, who has 13 caps for Germany at the age of 21, will be in their World Cup squad and have a significant impact for the national team long term.
"He [Julian Brandt] has got a great chance [of making Germany's World Cup squad]," Voller added. "Independently from being part of the national team's last few games, he is part of the future of Germany and in the national team.
"There is a lot of competition in his position, but his progression is trending upwards, he is the future of the national team and I would wish for him and for all of us, that he'd take part and have a good World Cup."