The Twins’ piece of the blockbuster Mookie Betts trade has reportedly stalled the rest of the deal, plunging Minnesota’s acquisition of Dodgers righthander Kenta Maeda into doubt on Wednesday, a major league source confirmed.

Talks are continuing, the source said, and the deal could still be salvaged. But a review of Brusdar Graterol’s medical records by the Red Sox has raised issues that the teams are working to resolve.

Graterol, the Twins’ top pitching prospect, was expected to be sent to Boston in exchange for Maeda, according to details of the three-way deal that became public one day earlier. But medical and paperwork issues slowed down its completion, and Graterol’s status could scuttle the deal.

The Twins, mindful of Graterol’s 2016 elbow surgery that kept him off the field for 15 months, and a shoulder impingement that sidelined him for two months last summer, had planned to limit the righthander to short bullpen stints, at least in 2020. But according to a report in The Athletic, the Red Sox acquired Graterol with the understanding that the 21-year-old Venezuelan could return to his former role as a starting pitcher.

The Red Sox apparently changed their mind upon receiving Graterol’s medical records, The Athletic reported, and now view him as a likely bullpen arm, a less valuable asset than a starter. Because of that, the report said, Boston has held up completion of the trade — perhaps to ask for more from the Twins or Dodgers.

Graterol, who has been working out regularly at the Twins’ spring complex in Fort Myers, Fla., did not throw on Wednesday as he awaits final word on whether he will join Boston.

The proposed trade was to have sent Betts, the 2018 American League MVP, and David Price, the 2012 AL Cy Young Award winner, to Los Angeles, with the Red Sox agreeing to pay half of the remaining $96 million due Price over the next three years. In return, the Dodgers were to send Maeda, a 31-year-old righthander who has won 47 games in his four-year career, to Minnesota, and outfielder Alex Verdugo to Boston.

No team has officially announced the deal, however, and none of the players has been notified while executives double-check medical records. In addition, MLB reviews all transactions that include such large sums of money.

The deal is an effort by the Twins to shore up their starting rotation. Maeda is expected to join Jake Odorizzi, Jose Berrios and Homer Bailey in the rotation this season, joined by Michael Pineda when his drug suspension ends in May, and free agent Rich Hill, likely out until July as he recovers from elbow surgery.

Graterol’s elbow surgery was in 2016, when he was 18. The righthander returned in mid-2017 and soon became a dominant starting pitcher in the low minors, with fastball velocity routinely surpassing 100 mph. He reached Class AA last summer but was shut down in May after experiencing shoulder soreness. When he returned in August, the Twins moved him to the bullpen to limit his workload, then called him up to the majors in September. The rookie appeared in 10 games, for a total of 9⅔ innings, and struck out 10 while posting a 4.66 ERA.

Pitching coach Wes Johnson said last month that Graterol would remain a reliever for the time being, and could make the major league team during spring training.