D.C. United has agreed to trade attacker Chris Pontius, the club’s longest-serving but oft-injured player, to the Philadelphia Union for financial considerations, multiple sources said Tuesday.

Meantime, United is on the verge of acquiring forward Lamar Neagle from the Seattle Sounders for financial considerations, known in MLS as allocation money, which can be used to help off-set the impact of a contract on the salary cap.

Neagle, 28, has played six years in MLS and recorded 21 goals and 15 assists in the past three regular seasons.

In essence, United is replacing Pontius ($365,000 base salary this year) with Neagle ($165,000).

Pontius, 28, completed his seventh season this fall with three goals and one assist in 23 league matches (17 starts). He missed most of the summer with a calf ailment. In the playoffs, he scored the tying goal in an eventual 2-1 first-round victory over the New England Revolution, then missed both legs of the Eastern Conference semifinals against the New York Red Bulls with hamstring tightness.

Since Pontius recorded 12 goals and four assists in 2012, a campaign that earned him Best XI all-league honors, a variety of injuries limited him to 51 regular season appearances (39 starts) the past three years. United had selected him in the first round of the 2009 draft, seventh overall, from UC Santa Barbara.

Aside from constant injuries, Pontius carried a high salary: With guaranteed compensation of $396,000 this year, he was fourth on United’s payroll behind forwards Fabian Espindola and Alvaro Saborio and goalkeeper Bill Hamid.

With a contract option for 2016, United had four choices: exercise the option and keep him on the books at about $420,000 overall; exercise it and then trade him; decline the option and renegotiate a lower salary; or decline the option and allow him to make himself available in the re-entry draft without the team receiving compensation.

According to sources, who did not want to be identified because the deal probably won’t be announced until next week, United did offer Pontius a new deal for between $250,000 and $300,000. Philadelphia, however, was willing to take him at the $420,000 rate. So United exercised the option and consummated the trade. The Colorado Rapids were also believed to be interested in him.

The Pontius deal was first reported by Goal.com. Teams are not allowed to comment on trades until after MLS Cup, which will take place Sunday in Columbus between the Crew and Portland Timbers.

Aside from the money, sources said, Pontius was looking for a fresh start after seven seasons in Washington. United was eager to open salary cap space in order to make additional moves this winter. It was also apparently concerned that Pontius’s health issues could linger for the rest of his career.

Both sides “knew it was time to move on,” one source said. Pontius “needed something different.”

Only three other players have been with United for at least five consecutive seasons: Hamid (six), defender Chris Korb (five) and midfielder Perry Kitchen (five), who is a free agent and might end up signing overseas. Sources said last week that United and Kitchen are “pretty far apart” in contract negotiations.

Neagle is a native of the Seattle-Tacoma area who played at the University of Nevada-Las Vegas and posted career highs in goals (nine) and assists (nine) in 2014.

Meantime, General Manager Dave Kasper was scheduled to begin a scouting mission in Argentina this week and then travel to Europe.

United, which faded late in the season after sitting atop the conference standings much of the year, knows it “needs to get better” this offseason, one source said.