With training camp heading into the final stretch, D.C. United is moving closer to filling the last roster slots and, it appears, nearing a new contract for 2011 MLS MVP Dwayne De Rosario.

Several trialists will remain with the club for the third stage of camp in Charleston, S.C., beginning Wednesday. “During or shortly thereafter, we’ll make roster decisions,” General Manager Dave Kasper said.

United just completed a 10-day session in Arizona and will practice in Washington early next week before traveling to Charleston for the four-team Carolina Challenge Cup.

Talks with De Rosario, who is entering the final year of his contract, are “on-going and remain positive,” Kasper said.

At the moment, United is able to apply allocation money — which is essentially MLS financial credits — to prevent De Rosario from being classified as a “designated player.” He would still earn DP money, which is beyond the 2012 MLS threshold of $350,000, but United would avoid a $250,000 league luxury tax for employing a third designated player.

If a new deal is reached, however, “it remains to be seen” whether United would be able to avoid the DP issues, Kaper said.

Toronto FC, one of De Rosario’s former clubs, covered a chunk of his $500,000 earnings after United acquired him last summer. This year he is completely on United’s books.

United is already paying designated player expenses for midfielder Branko Boskovic and newly acquired striker Hamdi Salihi.

The club acquired additional allocation money from the Portland Timbers this month in exchange for an international player slot.

MLS distributes allocation money for, among other things, missing the playoffs.

On a side note, the salary cap this year is $2.81 million, which applies toward 18 to 20 players. The rest of the roster is exempt.

[For the 2012 roster rules, click here.]

United is hoping Salihi, an Albanian who most recently played for Rapid Vienna, is approved for a work visa in the coming days and arrives in time for the start of the Charleston camp. United will play three matches in the tournament, which serves as the final tune-up before the season opener March 10 against Sporting Kansas City at RFK Stadium.

United currently has 23 players under contract and is likely to sign four more before the opener, Kasper said. United is in talks with former Chicago Fire goalkeeper Andrew Dykstra (Osbourn Park High School, Virginia Commonwealth University), who has been in camp for a month and is in line for the third slot on the depth chart.

Kasper declined to discuss the status of the other trialists, but rookie midfielder Lance Rozeboom, who scored in Tuesday’s friendly against Real Salt Lake, and defender-midfielder-forward Ryan Richter appear to be in good standing.

Others under consideration are midfielder Seth C’deBaca (Georgetown) and Brazilian forward Alfred Martins, 19, who began workouts a few days ago and will remain on trial in South Carolina. A second young Brazilian will arrive this weekend; Kasper declined to identify him until his paperwork is set.

Also, the Insider has learned the club is planning to look at a left back, where United lacks depth.