Wallabies suffer huge blow ahead of Ireland Test
Genia injured his knee during the Rebels' 55-10 Super Rugby defeat to Crusaders at the AAMI Park.
The star scrumhalf limped off the field just before halftime.
According to Fox Sports, the 30-year-old sustained a medial ligament tear, which means he is likely to be sidelined for up to eight weeks, ruling him out of the series against the Irish starting in Brisbane on June 9.
Genia already missed two previous Super Rugby matches because of a hamstring injury.
"At this stage, it looks like a grade two or three tear according to the physio," the Rebels spokesman told Fox Sports.
Genia will have a scan on Saturday to determine the severity of the injury.