The news came after the Samurai Blue's 1-1 draw with Australia, as Kagawa finally commented on his future after the important World Cup qualifier.
"I have to do a medical check but the agreement between me and the club is done," he told Japanese reporters.
"I wanted to avoid people focusing on this matter [during World Cup qualifiers]. It was Manchester United who sent me an offer officially."
The midfielder spoke to Sir Alex Ferguson ahead of his proposed moved to Manchester and revealed his delight following his conversation with the 70-year-old manager.
"It was great that such a great person spoke to me. I will decide my future soon talking with my agent. Then you will see the official news," he added.
"The agreement has been almost done. I asked myself to consider many things but I found that I want a challenge."
The move to Old Trafford looks set to see Kagawa become the first Japanese player to ever represent Manchester United, after two extremely successful years in Germany.