The 31-year old De Aza was acquired on Wednesday from the Baltimore Orioles for a minor league pitcher and cash.
To make room on the roster, the team designated outfielder Carlos Peguero for assignment.
De Aza appeared in 30 games for the Orioles, batting .214 with three homers and seven RBIs. He was designated for assignment on May 27.
The 28-year old Peguero was acquired from the Texas Rangers on May 27. He went 1 for 5 in four games with the Red Sox.