“Dealing with the exploitation of smugglers and unscrupulous agencies will finally come to an end for the Cuban baseball player,” Abreu said in a statement released by M.L.B. and the players’ union. “To this date, I am still harassed.”

M.L.B. and the Cuban baseball federation have been in talks ever since the United States and Cuba began a thaw in relations under the Obama administration in 2014. Soon after that, baseball’s commissioner’s office secured a license from the Treasury Department to legally commence negotiations with the Cubans.

On March 22, 2016, the Tampa Bay Rays played an exhibition game in Havana, attended by President Barack Obama during his visit there, with the long-term goal of encouraging an agreement on the free movement of players. But normalization of relations between the countries has slowed under the Trump administration, and some current administration officials have expressed reservations to M.L.B. and the players’ association about doing business with Cuban entities while a trade embargo, enacted more than 50 years ago during the Cold War, remains in place.

While the Trump administration bristled at the plan, an M.L.B. official noted that in a National Security Presidential Memorandum from June 2017, the government indicated it did not want to affect any existing approvals with Cuba; M.L.B. was granted approval the previous year.

One of the hurdles has been the restriction on money going into Cuba. The policy of the American government has been to allow financial support for everyday Cubans while keeping dollars out of the hands of the Cuban government or military.

Another possible sticking point: The Cuban federation, which is required under Olympic rules to be independent of the central government, can still prevent younger players from leaving Cuba before they reach their 25th birthday or have six years of service time. That would leave those players vulnerable to the dangers of human trafficking if they sought to defect.

This has complicated negotiations between M.L.B. and the Cubans. In the posting agreement with Asian countries, younger players are also prevented from joining M.L.B. teams, but they do not live under authoritarian governments, and M.L.B. was wary of entering into an agreement that would still trap young players who did not want to stay in Cuba.