Leverkusen signed Ballack on a free transfer from Chelsea earlier this week, bringing the 33-year-old back to the club he represented between 1999 and 2002, and director of sport Voller is now optimistic about his side's chances of glory next season.
"We were just lacking something and I think that Michael is that," he told the Sonntags-Express newspaper.
Leverkusen led the Bundesliga for two thirds of last season, going unbeaten until midway through the second half of the campaign.
However, like in previous years, they fell away in the end and only qualified for the Europa League.
Voller suggested that his side just lacked a bit of experience to match the likes of champions Bayern Munich and challengers Werder Bremen, but with Ballack now on board, they have the right mixture in the squad.
"Ballack should be a reference point in the team," explained the 1990 World Cup winner. "He is the ultimate lead figure."
Nevertheless, Ballack is unlikely to become captain at the Bundesliga club since Simon Rolfes has done a good job in that role, but even without the armband, Ballack "can lead a side", according to Voller.