Midfielder Mohammed Abu is expected to be available for Saturday afternoon’s match at Audi Field against expansion Inter Miami, while attacker Federico Higuaín will continue fitness efforts before debuting this spring.

Both moves were in the works for weeks and not announced until after the season started — notable acquisitions that, in most U.S. pro sports leagues, might not have occurred at such a late point.

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The NFL has cutdown dates, the NBA finalizes squads on the eve of the first games, and Major League Baseball teams set Opening Day rosters as spring training ends. In MLS and in soccer leagues worldwide, there is no ceremonial day to unveil the squad.

It’s different in soccer because of the number of mechanisms to acquire players (transfers, loans, trades, free agency and homegrown signings), the global talent pool and signing deadlines that extent beyond the first match.

“We will be so different in the summer than we are right now, and down the stretch we’ll be a completely different team,” United Coach Ben Olsen said. “We talk about this being a journey, and there are so many twists and turns in how we play and with the personnel.”

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Before the openers, MLS teams had to adhere only to salary guidelines and roster limits. United and others left room in both categories to continue making moves.

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The first MLS deadline is not until May 5, the end of what is known as a transfer window, which pertains to deals with clubs abroad and intra-league trades. Free agents remain fair game until rosters are frozen Sept. 1 — about a month before the regular season ends.

Major European leagues also allow moves several weeks into the season and reopen the window for a month midseason.

MLS’s second transfer window will run July 7-Aug. 5.

United began the season with 23 players under contract; the maximum is 30. Abu and Higuaín filled two slots, and the organization is hoping to acquire two defenders before May 5.

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It is a complicated process when teams are chasing players abroad as United is. Most leagues run from August to May, so as MLS is getting started, many clubs abroad are engaged in tense races — for trophies, for qualification into continental tournaments, for promotion to a higher division and for avoiding relegation to a lower flight.

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“We are in a situation now where we have a few players on our radar, and some of these players are in promotion or relegation battles,” Kasper said. “Clubs say, ‘Listen: Whenever we get through these situations and have clarity, we would be happy to negotiate, but right now we can’t. We need these players.’ ”

Kasper did not go into specifics, but people close to the situation said United hit a roadblock in trying to acquire defender Bakaye Dibassy from French club Amiens, which is second to last in Ligue 1 and in danger of being relegated.

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United will have to decide whether to wait for Amiens to change its mind before May 5 or pursue other leads. It also could put the Dibassy pursuit on hold until the summer window.

United has only three center backs, including Donovan Pines, who is recovering from an ankle injury.

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“You have to go down parallel paths with multiple players,” Kasper said. “It’s the nature of the game. Every weekend, we have a tracker, following teams, trying to predict when we think players will become available.”

While the winter window is complex in acquiring European-based players, it accommodates MLS teams seeking talent from Latin America, where split seasons typically wrap around the holidays. Latin America has become the primary resource for MLS teams, who this winter signed several players from Mexico’s Liga MX.

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The greater global player movement, though, occurs in summer, when most leagues are dark and player contracts expire.

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United might sign a high-priced designated player this summer. “It’s in the mix,” Kasper said, “if we find the right opportunity.” United employs two DPs (Arriola and Edison Flores), leaving one slot vacant.

“It’s definitely more fun shopping in the summer than in the winter, but there is always opportunity to tweak the roster,” Olsen said. “It’s tricky, but that’s why we have a GM who is very well versed in this stuff, so I can worry about coaching.”

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Notes: Canouse and defender Steven Birnbaum each signed a contract extension through the 2023 season. …

Ulises Segura, who started on the left wing in the opener, is questionable with a minor groin injury. Emmanuel Boateng and Yamil Asad, who missed most of preseason with a groin injury, are the other primary options.

Inter Miami at D.C. United

When: Saturday, 3:30 p.m. (3:50 kickoff).

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Where: Audi Field.

TV: Univision.

Records: United 0-1-0, Inter 0-1-0.

D.C. probable starters: GK Bill Hamid; D Russell Canouse, Frédéric Brillant, Steven Birnbaum, Joseph Mora; MF Felipe Martins, Júnior Moreno, Julian Gressel; F Edison Flores, Ola Kamara, Emmanuel Boateng.

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Miami probable starters: GK Luis Robles; D Alvas Powell, Román Torres, Nicolás Figal, Ben Sweat; MF Lewis Morgan, Wil Trapp, Victor Ulloa, Rodolfo Pizarro, Matías Pellegrini; F Robbie Robinson.