The Union traded midfielder-defender Amobi Okugo, the only player who had been with the team since its inception in 2010, to expansion Orlando FC on Monday for a second-round pick in 2016 and allocation money.
The Union also acquired forward C.J. Sapong from Sporting Kansas City for their highest pick in the 2015 MLS SuperDraft.
Sapong, 25, had 20 goals and nine assists in four seasons with Kansas City. He was a regular early in his career but had just seven starts and two goals last season.
The Union are hoping Sapong can revive his career similar to forward Andrew Wenger, who had six goals and four assists after he was acquired from Montreal in April.
Okugo, 23, said in a telephone interview that he looked at the option of playing in Europe but is now committed to staying in the MLS.
"Europe was a viable option, and after looking and assessing all options, Orlando was the best situation," Okugo said.
Among the most popular Union players, Okugo appeared in 117 games, 101 as a starter, and totaled five goals and six assists. Last season, he was among the team's top players with two goals and two assists in 32 games, including 31 starts.
Okugo said he will miss the fans.
"I would like to say, 'Thank you,' to the fans for their loyalty and passion for five years I was there," he said. "I am sorry I wasn't able to be part of a team to give the fans their first trophy."
The Union also declined the contract options on five players, the most notable being forward Conor Casey, who had 18 goals and seven assists in two seasons.
The others were midfielders Corben Bone and Fred and forwards Brian Brown and Cristhian Hernandez. Additionally, midfielder Brian Carroll's contract expired.
The Union are preparing for Wednesday's MLS expansion draft, with Orlando and New York City FC selecting players. MLS teams can lose no more than two players, and they can protect 11. Once a player has been claimed from a club's nonprotected roster, the team can protect another player.