Cabrera, 29, agreed to the contract before Christmas, but the team is waiting to have him undergo a physical exam because of the holidays, the source said.
A two-time All-Star, Cabrera batted .229 with five home runs and 21 RBIs for the Nationals in 49 games after the trade. In total, between both teams, he finished last season batting .241 with 14 homers and 61 RBIs.
Cabrera has a career average of .268 with 87 homers and 451 RBIs in eight seasons with the Indians and Nationals. His best season was 2011, when he hit .273 with 25 home runs and 92 RBIs.
He was paid $10 million in 2014.