Unhappy with frontline production, D.C. United on Thursday acquired Colombian forward Lionard Pajoy from the Philadelphia Union for midfielder Danny Cruz. United also received an international roster spot, which was needed to accommodate Pajoy’s acquisition.

Pajoy, 31, has five goals and two assists in 20 appearances during his first season in MLS. He joins a striker corps with significant issues: Maicon Santos (seven goals) is out with a toe injury, Hamdi Salihi has not met expectations after signing a major contract in preseason, and newly acquired Long Tan hasn’t scored in three appearances since arriving from Vancouver.

“Right now, Pajoy fits pretty high” on United’s depth chart, Coach Ben Olsen said. Presumably, Pajoy would partner with withdrawn forward Dwayne De Rosario, who is tied for second in MLS in assists with 10 and has scored five times. The 2011 league MVP missed his first game of the season last week because of a shoulder injury but is expected to return to the lineup this weekend.

“They’ve all done fine,” Olsen said of Santos, Salihi and Tan, “but we needed to add another option and another piece up top. Pajoy complements a lot of our guys.”

Pajoy is scheduled to join the club Friday and might end up starting Sunday, when United (11-8-3) faces the Union (7-12-2) at RFK Stadium.

The trade was the second in eight days by United, which acquired defender Mike Chabala from the Portland Timbers for a supplemental draft pick.

United has lost four of six matches and slipped to fifth place in the Eastern Conference. The top five will earn playoff berths, and having played fewer games than all but one of the other contenders, D.C. is in good position to end a four-year playoff drought.

However, United was once among the league’s top-scoring teams but has just two goals in the past four regular season matches: by Chris Pontius, who is most effective on the left side of midfield, and wide midfielder Nick DeLeon.

To acquire the 6-foot-1 Pajoy, United relinquished Cruz, a personable character who brought energy and grit to the midfield since joining the club from the Houston Dynamo last winter. Cruz, 22, won a starting job early this season, but in recent weeks, his playing time diminished. He didn’t enter either of back-to-back matches against the Columbus Crew and played just 10 minutes during last Saturday’s 2-1 loss at Sporting Kansas City.

Cruz said last week that he was becoming increasingly frustrated with his role. On Thursday, after being told about the trade before practice, he said: “I wasn’t playing much, I was obviously unhappy, but I didn’t ask for a trade. When they called me in this morning, I didn’t expect it.”

Cruz added: “I am thankful to D.C. United — there’s no ill-will.”

Olsen said Cruz became expendable because United has a “luxury of riches” at the wide midfield positions. Pontius is United’s leading scorer with 10 goals, DeLeon (four goals, three assists) is enjoying a quality rookie season, Andy Najar has rejoined the club after Olympic duty with Honduras and English veteran Lewis Neal has provided support on the left side.

That said, “It’s hard trading a guy like Danny,” Olsen said. “I like Danny, and he has had a real impact on the team and the community” in terms of fan outreach.

Asked if Cruz’s frustration was spilling over in the locker room, Olsen said: “I don’t think it affected the group that much. Who’s happy when they’re not playing? He’s an emotional kid but it was never a detriment.”

The exchange will impact United’s payroll. Cruz’s base salary was $100,000, while Pajoy earns $180,000 annually.

Pajoy has scored 47 goals in 215 appearances since beginning his career with Colombian club Cortulua in 2004. He also played in his homeland for Atletico Huila in 2005, Boyaca Chico in 2006, Deportivo Cucuta from 2007 to ’09, Deportivo Cali in 2010, and Millonarios in 2010 before a loan to Itagui Ditaires last year.

“We felt that we needed to add another piece up top and the opportunity to get Lionard Pajoy was one that we could not pass up,” General Manager Dave Kasper said in a written statement. “We’re excited to integrate him into our side immediately.”