England will be without Geoff Parling for the November internationals after the lock was sidelined with concussion.
The Leicester Tigers forward was replaced during his club's 45-0 defeat to Bath on September 20 after suffering a blow to the head at the Recreation Ground.
It was the second time in three games the 30-year-old had been substituted with concussion and as a result he was referred to a specialist.
Following that consultation, Parling has been advised to rest to ensure he recovers fully and does not suffer any further complications from the two blows.
Leicester director of rugby Richard Cockerill confirmed Parling will not feature until December, meaning he will miss matches for the national side against New Zealand, South Africa, Samoa and Australia.
"Geoff saw the relevant specialist this week and will have time out of the game now," said Cockerill.
"He'll probably have three or four weeks of complete down time and then he'll be reintegrated into training.
"You'd like to think that by December he'll be playing again. And there's no doubt about that, he will play again, there are no issues over that.
"It's more that he's had successive concussions in a short period of time. You have to take that very seriously, as we do.
"Ultimately there are more important things than playing rugby and you have to look at the bigger picture."
Parling joins Alex Corbisiero, Tom Youngs (both shoulder), Mako Vunipola (knee) and Dan Cole (neck) on the sidelines for England, while Owen Farrell (thigh strain) remains an injury concern.