Betts was traded from Boston to Los Angeles on Tuesday in a three-team deal. The Dodgers were slated to receive Betts and starting pitcher David Price, and the Minnesota Twins were to receive starting pitcher Kenta Maeda. Graterol joined outfielder Alex Verdugo in the return to Boston, though his physical is reportedly freezing the deal.
"The Red Sox, sources said, were spooked by a medical review of Graterol, the hard-throwing 21-year-old right-hander who has undergone Tommy John surgery and missed time in 2019 because of a shoulder injury," Passan wrote late on Wednesday night.
Graterol's physical is unlikely to torpedo the trade, as the three teams "remain confident it will be completed," per Passan. A different prospect could be sent to Boston, or the Red Sox could reduce the money they are paying Los Angeles to cover part of Price's $96 million contract.
MLB Network's Jon Heyman reported Thursday evening that the Red Sox were still trying to reconfigure the part of the deal involving the Twins. He adds that that while there is still hope the deal gets done in some form, some involved are "now suggesting it's not a certainty."
Betts is a four-time All-Star and the 2018 American League MVP. The 27-year-old outfielder has led the AL in runs in each of the last two seasons, and he posted a league-high .640 slugging in 2018. Betts and the Red Sox beat the Dodgers to win the 2018 World Series.
Graterol is currently baseball's No. 83 prospect, per MLB.com.