However, although the Bundesliga club would be interested in bringing Ballack back, they are also realistic about their chances of pulling off what would be a major transfer coup.
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"Michael had a great time here and we have remained in contact over the years.
"We are relaxed about it all, but Michael Ballack is an issue we are dealing with, particularly since he would like to return to Germany."
Ballack's wages could be the stumbling block to a return to the Bundesliga since only his former employers Bayern Munich can realistically afford the salary he was on at Chelsea.
But Leverkusen hope Ballack would be willing to compromise.
"Normally a player like Michael is out of reach for us," admitted Voller in the Express newspaper.
"A transfer would only be possible if the player accepted a pay cut."
Schalke and Wolfsburg have also been linked with the 33-year-old Germany captain, who misses the World Cup this summer due to an ankle injury.