London - Ulster's South African captain Johann Muller will be out of action for eight weeks after breaking his arm in the 25-6 win over Northampton in the European Cup.
"An x-ray this morning (Saturday) revealed that he has an undisplaced fracture and he is expected to be out for at least eight weeks," said an Ulster statement.
Lock forward Muller only recently returned to action after missing six weeks with a thumb injury.
Ulster's win at Franklin's Gardens on Friday maintained their perfect record this season as they won their 13th successive match.
The 32-year-old Muller played 24 Tests for the Springboks between 2006 and 2011.