Michael Ballack has long been rumored to be eyeing a potential move to Major League Soccer. Those rumors have recently picked up steam, largely because of news that his current club, Bayer Leverkusen, is open to granting his release (via ESPN). In that same story, it's said that Ballack is considering a move to MLS, China or Saudi Arabia.
Other reports have suggested the New York Red Bulls, Montreal Impact, Chicago Fire, Philadelphia Union and Seattle Sounders have all expressed interest in the midfielder. Sounders GM Adrian Hanauer has already gone on record as saying his team is not pursuing Ballack, and the Union have previously expressed disinterest in adding aging players. That would seem to leave the Red Bulls, Fire and Impact as Ballack's most likely suitors.
Of those teams, the Red Bulls and Impact are the only two that would really make any sense. Ballack is said to be looking for somewhere in the neighborhood of $6 million a year and the Fire have never paid anyone close to that amount.
The Impact have been pretty open about their pursuit of a Designated Player and Ballack would certainly be the kind of signing that would pique interest. Whether or not he has anywhere close to the ability that would justify such a massive price tag is very much an open question.