The 31-year-old All Blacks prop will miss the Cherry and Whites crunch Pool 6 ties with Cardiff Blues and Biarritz after undergoing eye surgery.
Somerville was hurt during last weekend’s Guinness Premiership defeat by London Irish and had surgery in Cheltenham to re-attach the retina in his left eye.
Gloucester Dean Ryan said: “It’s a nasty injury and will take some considerable recovery time.
“We will obviously miss his contribution as a world-class player, and we wish him a speedy recovery.”
Somerville, capped 66 times by New Zealand, has played just once in the Heineken Cup as a replacement in the home win over Calvisano since joining Gloucester earlier this month.
