D.C. United’s technical staff spent the past several days in South Florida watching the college combine. Their priority this winter, however, has remained focused on proven players, not prospects.

So on the eve of the MLS draft, United continued bolstering its roster Wednesday by acquiring Costa Rican forward Jairo Arrieta from Orlando City for an international roster slot.

Arrieta, 31, is entering his fourth season in MLS after starring in his homeland and making periodic national team appearances. He is the second veteran procured by United this week, joining Finnish national team midfielder Markus Halsti , 30, who arrived with UEFA Champions League experience at Swedish club Malmo.

United is building toward not only the regular season opener March 7 but the CONCACAF Champions League quarterfinals against Alajuelense (Costa Rica) on Feb. 26 and March 4. Training camp will open late next week.

“We are going to go from zero to 100 very quickly,” General Manager Dave Kasper said. “The early part of the year is going to be very busy, and it’s important to get guys who are ready to contribute right away.”

Arrieta scored 17 goals in three seasons with the Columbus Crew before Orlando claimed him in the expansion draft last month. In Washington, he will join a front-line corps that will go without Fabian Espindola for the first six regular season matches. Espindola, the 2014 co-leading scorer, was suspended by MLS for shoving an assistant referee at the end of the playoff finale.

Espindola’s absence for a large chunk of the 34-game league schedule factored into the Arrieta trade, Kasper acknowledged, but so did the Champions League slate. Arrieta accelerated his career over six years with Saprissa, Alajuelense’s rival, and featured on the national team. (He was on the preliminary roster for the 2014 World Cup but did not make the final squad.)

With the Crew, Arrieta posted nine goals and four assists in 18 regular season matches in 2012. He had three and four, respectively, in 26 games in 2013 and five goals and one assist in 23 matches (14 starts) last year.

Arrieta is a permanent U.S. resident and does not count against MLS’s international player limit. He earned $135,000 last season.

As for the draft, United will pick 17th and 42nd overall in the first two rounds, which MLS will conduct Thursday at Philadelphia Convention Center. The last two rounds are Tuesday via conference call. Kasper said United is “not actively looking to move up” but has fielded offers for the No. 17 slot for multiple picks.

United does need to acquire a third goalkeeper, but Kasper said he already has invited two candidates to training camp and probably will not select a college-age keeper. He declined to identify the players coming for tryouts.

With midfielder Andrew Driver and forward David Estrada unsigned, United might look to the draft for attacking depth. Driver was acquired from Houston for goalkeeper Joe Willis and defender Samuel Inkoom, presumably to fill a prominent role this season.

However, “at this point, we’re going to evaluate where we are after the draft,” Kasper said. Signing Driver and Estrada “could happen, or it might not.”

Midfielder Rod Dyachenko, who served with D.C. in 2006 through 2008 and has played in Thailand for three years, was invited for a tryout.