Mark McCall, Saracens director of rugby, said: "For any team to lose a player of the ability of Maro is a blow and he will be missed through the autumn for both Saracens and England.
"What's now important for Maro is his recovery and we look forward to his return later this season."
The 21-year-old Itoje, who had an X-ray and saw a specialist following the injury, had been earmarked by England coach Eddie Jones to switch from lock to the problem position of flanker, where James Haskell, Jack Clifford, Mike Williams and Sam Jones have already been lost to injury.
England's autumn series begins against South Africa at Twickenham on Nov. 12. England also play Fiji on Nov. 19, Argentina on Nov. 29 and Australia on Dec. 3.
(Reporting by Neil Robinson; Editing by Ian Chadband)
