The deal includes an option for United to purchase him outright after the 2016 MLS season.

United prioritized central midfield this winter, and in acquiring the 5-foot-3 Acosta, the club appears to have added a dynamic, young piece to a veteran lineup. Acosta served with Boca Juniors in 2013-14, then moved to Argentine club Estudiantes on loan last year, appearing in 27 league matches (11 starts) and seven Copa Libertadores games.

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United showed interest earlier this winter, but with Boca planning to loan him to Brazil’s Coritiba, talks went nowhere. However, while United turned attention to Estudiantes’ Leonardo Gil and other targets abroad, Boca reached out to United and revived discussions last week.

Acosta would become the fourth potential new starter, joining wings Lamar Neagle and Patrick Nyarko and central midfielder Marcelo Sarvas.

Meantime, United is pivoting away from signing AC Milan midfielder Antonio Nocerino and engaging in talks with Orlando City about trading the former Italian national team player’s MLS rights, one source said.

Both clubs were interested in signing Nocerino, 30, but United was first to submit a discovery claim, which affords exclusive negotiating rights among MLS teams. During the talks, however, Orlando allegedly made an offer, a violation of MLS tampering rules. Because Orlando was prepared to tender a larger salary, Nocerino had second thoughts about signing with United.

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United has declined to match Orlando’s offer, telling sources it wanted to preserve resources for other signings.

The situation has apparently reached the point where Nocerino would only come to MLS if it’s to the highest bidder (in this case, Orlando). With that in mind, United has apparently fielded trade offers from Orlando City. Signing Nocerino would reunite the Italian with his former AC Milan teammate, Kaka, who is entering his second season with the Florida organization.

Asked where things stood with international targets, United Coach Ben Olsen said: “We’re talking internationally all the time. My phone bill is getting up there.”

Without specifying, he did concede that the team was “getting close” to acquiring a player from abroad.

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He also said United would sign “one for sure, two possibly. … We’re still dealing with other internationals. We still have some needs. We have a little money to spend.”

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Meantime, United cleared space on the senior roster Tuesday by trading reserve forward Conor Doyle to the Colorado Rapids for a 2017 third-round draft pick. Doyle, 24, joined the club on loan from England’s Derby County in the summer of 2013 and made a permanent move after the season.

In 56 regular season appearances, he made 19 starts and scored four goals. The Texas native missed the last three months of the 2014 season with a knee injury. His primary role the past two years was to enter in the late stages, apply high pressure and chase the ball from side to side. Last summer, he scored a thunderous late goal from distance for a 1-0 victory at Chicago.

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“Conor is always a guy you want on your team, but at a certain point, it’s important for him and for us to move guys on if they are not going to get the minutes that we think can move them along in their career,” Olsen said. “He was a reliable piece and really helped us the last couple of years in a lot of different situations, but there is an opportunity in Colorado.”

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United might end up filling his roster slot with Rob Vincent, a 25-year-old English attacker from the third-division Pittsburgh Riverhounds. He has been on trial with United since the start of training camp. Aside from reaching a contract deal, United would have to purchase his rights from the USL club.

“He has been sharp,” Olsen said, “but there is a lot of competition for roster spots.”

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Five other trialists survived the first cut last week and probably three others will begin workouts in the second stage of camp, which starts late this week in the Tampa area. Olsen did not identify the newcomers, other than to say they are a goalkeeper and two midfielders.

United is seeking an experienced goalie to compete with Andrew Dykstra for the starting job while first-choice keeper Bill Hamid recovers from a long-term knee injury. Chris Konopka, Toronto FC’s starter for 21 matches last year, remains in camp. Travis Worra, entering his second season, is expected to fill the third goalkeeping slot.

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Dykstra is almost certain to start against Queretaro in the Champions League.

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“We believe he’s ready for it,” Olsen said. “He’s had a good camp. He is miles ahead of where he was at this time last year [when he was just back from an Achilles’ injury]. He is going to get a lot of reps in preseason. He has always been reliable for us and we don’t see why this would be any different.”