Howell joined Quins from Canberra
Harlequins centre David Howell has been ruled out for the rest of the season after fracturing an eye socket.
The Australian was injured in training last week and will miss his side's push for the Super League play-offs.
Meanwhile, forward Ryan Esders will stay with the club to the end of the campaign after extending his loan deal.
The 22-year-old, who has scored two tries in five games, joined Harlequins from Super League rivals Hull KR on an initial one-month deal in July.
Quins head coach Brian McDermott said: "Ryan Esders has fitted into the squad well and we're very pleased he'll be with us longer."