The Red Sox said Lavarnway fractured his hamate bone in Thursday night's win over Atlanta. He left the game in the fifth inning with what was originally called a sore wrist.
To take his spot on the roster, Boston recalled outfielder/first baseman Alex Hassan from Triple-A Pawtucket.
The 26-year old Lavarnway was recalled earlier in the week and went 0 for 4 in four games.
Hussan, 26, was promoted to the majors for the first time. In 45 games with Pawtucket this season, he hit .217 with one homer and 19 RBIs. He was born about 10 miles from Fenway Park, in Quincy, Massachusetts.