Nick Sakiewicz is out as the Union's CEO and chief operating partner. The team is expected to make the announcement on Friday.
CBSphilly.com first reported on Sakiewicz's departure.
Reached late Thursday by The Inquirer, Sakiewicz provided this statement: "I enjoyed my time at the Philadelphia Union and am proud of the team and organization and stadium we built," he said. "I wish the Union, [team chairman and owner] Jay Sugarman, and the entire organization the best of luck and continued success."
Sakiewicz said he didn't want to discuss anything further.
A source familiar with the situation said that the move had been brewing for some time and that the penalty-kick loss to Sporting Kansas City in the U.S. Open Cup final on Wednesday had no bearing on the decision. The Union lost, 7-6, in penalty kicks after the teams played to a 1-1 draw through 120 minutes.
Sugarman has stayed mostly behind the scenes while Sakiewicz has served as the team's spokesman on a variety of issues, from player personnel to marketing. It will be interesting to see whether Sugarman takes a more public role with the team.
The Union, who play at PPL Park in Chester, are completing their sixth MLS season. A former professional goalkeeper, Sakiewicz founded Keystone Sports & Entertainment in 2006 and assembled the investors who eventually became the ownership group of the Union.
The Union are 9-15-7 this year and will be eliminated from the postseason with a tie or loss Saturday at Toronto. They have just three MLS games left. The team has qualified for the postseason just once, during its second season, in 2011.
Last year, the Union fell to the Seattle Sounders, 3-1, in extra time in the U.S. Open final, also at PPL Park.
Sakiewicz has been the target of mounting social media criticism for the Union's struggles.
The Union have been the subject of other recent personnel rumors. The team denied a report earlier in the week by Empireofsoccer.com that said the Union would hire former MLS coach Octavio Zambrano as their technical director.