Saracens flanker Dave Seymour could be sidelined for two months after suffering a knee injury during the Guinness Premiership opener against Harlequins.
Seymour was forced off midway through the second half at Twickenham as Saracens went down to a 24-21 defeat.
Ligament damage has been diagnosed, with Saracens not expecting him back in action until late October or early November.
Saracens rugby director Eddie Jones said: “It is a blow for the squad and for Dave, who has trained very hard throughout pre-season.
“He was in good shape going into the start of the season, so it is obviously a massive disappointment for him.
“But he has already started his rehab, and it won’t be long before he is back in full training.”