The German midfielder spent five years at Dortmund before making a permanent £20 million move to Manchester City. However, if things went differently, he could have ended playing for their bitter rivals.
Gundogan told Sky Sports:
"There were talks. I think it was two or three years before I joined City when I was playing for Borussia Dortmund
"One team-mate of mine, Shinji Kagawa, went to Man Utd and someone told me that they came to a few games to watch him before they bought him. I took their attention.
"It never really went into advanced talks because Borussia Dortmund made it quite clear that they were not willing to sell me and I also had a few years left on my contract, so there wasn't really a point to talk to anyone at that point. So yeah, it didn't happen."
Currently at top of the table with a 10-point clearance, Manchester City will face West Ham on Saturday.