An academy product of the MLS side, he currently competes for the Union's reserve squad. However, the recent agreement will grant him the opportunity to participate in Major League Soccer and various other competitions for the first team.

Following several impressive displays, the teenager has attracted interest from a number of European clubs, with Pep Guardiola's Man City moving fast to secure his signature. Premier League regulations prohibit clubs from recruiting foreign players until they reach the age of 18. Consequently, Sullivan is expected to stay put with Philadelphia until he reached that said age in September 2027. 

"The collaboration between the Union and the City Group was, I think (the thing) that did it for me," Sullivan told ESPN. I always watch Man City. They're like every kid's dream team. For them to come together and agree on something, I sat with my family and my agents and we decided that it was the best plan.

"To be honest, nothing really has happened yet and the work starts now. I still have a lot to do. My main goal is to win MLS Cup, so development starts now. It does feel nice but there's still a lot of work to do for my part and a lot of room to grow."

Quinn, Sullivan's elder brother, currently competes for the Union's first team, while his two other brothers, Ronan and Declan, are enrolled in the club's youth academy. "I've been watching my home team, the Union, for as long as I remember and hoped that one day I'd get the chance to play for my city in front of my family, friends, and fans," Sullivan said in the club's statement.

"Being able to not only play for the Union but to be able to play with my brother is a dream come true. I will give everything I have to this club and hope to help bring home some hardware. I'm thankful for the opportunity and hope to make Philadelphia proud."

During a press conference, Union coach Jim Curtin opted not to disclose the timeline for the player's inaugural appearance for the first team. The record for the youngest player to debut in MLS is held by Freddy Adu, who made his first appearance at the age of 14 years and 306 days in 2004.

"Cavan is 14. His job here will be to be a kid and play and reach his full potential. Our job here is to create an environment where can thrive," Curtin said. "Cavan is a generational talent. That is not the opinion of just the Philadelphia Union. That is globally through scouts, clubs all over the world."