Boston made the moves Sunday.
Ross sustained the injury in Saturday's 3-2 loss to Toronto. He's hitting .209 with four homers and five RBIs in 15 games.
The 25-year-old Lavarnway is up with the Red Sox for the second time this season. He was promoted in late April, but did not see any action.
Lavarnway is hitting .313 with two homers and 15 RBIs for Pawtucket.