The midfielder, a three-time winner of the German Football of the Year award, joined Chelsea from Bayern Munich in summer 2006.
Before Ballack joined the Blues, the Red Devils had finished bottom of a Champions League group containing Villarreal, Benfica and Lille, while Chelsea had been crowned champions of English football.
He won the Premier League title and the FA Cup on three occasions in more than 150 appearances for the Blues.
But the retired enforcer did not taste European glory with the Stamford Bridge outfit.
And Sir Alex Ferguson’s men had the last laugh by lifting the trophy two years later at the expense of Ballack's Chelsea in Moscow.
Speaking exclusively in the April 2013 issue of FourFourTwo, the 36-year-old admits it was a decision based on ambition with the Blues on a seemingly upward curve.
"Yes, Manchester United wanted me, and it's a good question [why he chose Chelsea].
"They came before Chelsea, but I didn't have discussions with Sir Alex Ferguson.
"At the time United were not really good in the Champions League – they had gone out in the first round that year.
"But Chelsea were growing really quickly. I wanted to be a part of this. I saw we could reach something really big in the next few years."
Read the full, in-depth one-on-one interview with Michael Ballack in theApril 2013 issue of FourFourTwo, in shops now. The latest issue features Mario Balotelli's return to Italy with AC Milan and the making of Jose Mourinho, and chats exclusively to new Premier League sensation, Michu. If that' s not enough for your monthly football read, we've also gone inside talkSPORT for an in-depth look at the world of the football phone-in and grabbed an exclusive word with Schalke loanee Ibrahim Afellay.
Then there's Michel Salgado on doping, David Haye on Danny Shittu and stats on the world’s most prolific academies.
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