Mako Vunipola (Saracens prop) is expected out for 10 weeks after having surgery on an ankle injury.
A club statement stated that he would return to action in 8-10 weeks. He will therefore not be available for play until the penultimate round.
Vunipola started 15 matches for Saracens. They are currently second in the league with six games remaining.
He has won 67 England caps but has not played in a test match since being replaced as the Test captain. British and Irish Lions were beaten 19-16by the world champions in Cape Town, August to lose series 2-1.