Sullivan, who is approaching his 17th birthday, has already established himself with Philadelphia Union despite his age. The attacking midfielder has scored seven goals and provided five assists in 24 MLS appearances and became a professional at just 14.
His performances have also earned him a place in the United States national team under Mauricio Pochettino. Sullivan made his first international start against Peru on Saturday.
He can operate on either flank or in midfield and has also been selected several times in the MLS Team of the Week alongside Lionel Messi.
A pre-agreement had initially been reached with the City Football Group for Sullivan to join Manchester City when he turns 18 in 2028.
That arrangement is now facing uncertainty following the Premier League’s findings against Manchester City.
According to Sport, the outcome of the 115-charge case and the potential sanctions against City have created legal uncertainty around the proposed operation.
Sullivan’s agent, Dan Segal, has acknowledged that the preliminary agreement exists while leaving open the possibility of circumstances changing.
“Manchester City is one of the biggest clubs in the world. What they have built will remain forever in history,” Segal said.
“It is true that there is a preliminary agreement with them concerning Sullivan, but you never know what can happen. We hope they can resolve all of this in the best possible way.”
That uncertainty has attracted interest from elsewhere in Europe.
Barcelona and PSG are monitoring the situation closely, while Real Madrid are also reported to be following developments around the teenager.
For Sullivan, the interest comes after an extraordinary rise through the American game. He has been playing regularly since he was 15 and has continued to make an impact against senior opposition in MLS.
His combination of technical ability, versatility and production has made him a prominent figure in the next generation of American football.
The possibility of joining Manchester City remains tied to the preliminary agreement already reached, but the uncertainty surrounding the club has created an opening for other European sides to assess whether a deal could be reached.
Sullivan therefore faces an unusual situation for a player still only 16: his next club could involve a move to one of Europe’s biggest development programmes, but the original route to Manchester has become less certain.
For now, the midfielder remains with Philadelphia Union, where his performances continue to attract attention on both sides of the Atlantic.