Saracens have been dealt a second injury blow at scrum-half with the news Neil de Kock will be out for up to three months with a fractured arm.
The 32-year-old was injured in the Heineken Cup match against Treviso.
The Premiership champions are already without England international Richard Wigglesworth for the rest of the season following knee surgery.
Sarries will turn to 19-year-old Ben Spencer, who played the full 80 minutes in Saturday's loss against Biarritz.
It was Spencer's 10th Saracens appearance since he joined from National One side Cambridge in the summer and he will be in line to keep his place against Northampton Saints this weekend.
South African De Kock had to receive surgery on Monday to remove a metal plate from a previous injury, with the hope of aiding the current fracture to heal.
The 10-time capped Springbok had featured nine times this term.
Saracens also have 21-year-old Luke Baldwin as scrum-half back-up and the Sarries academy graduate will now hope to build on his two senior appearances for the club.
Meanwhile, the club have confirmed January's return clash with Biarritz will now take place at Vicarage Road.
The game had been planned for Cape Town, until a row erupted between the two potential host venues.