Now they are partnering with Union regarding young players, with 14-year-old Sullivan admitting as much.
He told ESPN: "The collaboration between the Union and the City Group... I think that did it for me.
"I always watch Man City. They're like every kid's dream team. For them (Philadelphia and City) to come together and agree on something - I sat with my family and my agents and we decided that it was the best plan.
"I guess my goal is just to become a regular player (for Philadelphia) within the next two years. And then after that I would hope to be a starter. I guess that's from the 16 to 18 age window. And then right when I'm 18 I hope to be at the level of the Man City first team."
His father is quoted as saying: "I think he's a pretty mature kid. I think he gets some of it. That's not to say we don't think there's going to be bumps along the way. We definitely know that.
"And I think that's part of the reason this collaboration between the Union and City Group is so important because he really does have a safety net here."