The Lions pair missed the two-day gathering, which started yesterday, as head coach Eddie Jones gets his last chance to see his team ahead of naming a Six Nations squad on January 18.
Wing Nowell was taken off with an ankle injury after 75 minutes of Exeter’s 30-6 win over Leicester on Sunday, while centre Joseph suffered a dead leg in Bath’s 31-26 loss to Wasps on Friday.
Other victims from the last round of the Premiership are Bath lock Charlie Ewels (hamstring), and Northampton fly-half Piers Francis and Exeter prop Harry Williams, who both suffered concussions.
Jones has called up Bath prop Henry Thomas and Joe Cokanasiga, the London Irish wing, for the south coast camp.
Thomas last played for England in New Zealand in 2014 and has just returned to action after double knee surgery.
Jones took the 20-year-old Cokanasiga on the summer tour to Argentina although the youngster did not see any match action.
The England head coach has already lost wing Elliot Daly, prop Ellis Genge and No8 Nathan Hughes for at least part of the Six Nations as the body count continues to rise.
But Billy Vunipola, who missed the autumn internationals with a knee injury, is in camp and is expected to be fit for Saracens’ trip to Wasps on Sunday.
The 25-year-old, who missed the Lions tour with shoulder trouble, has not played since September 23.
And Maro Itoje – another Brighton attendee – is also on course to be fit for Saracens duty this weekend after recovering from a broken jaw sustained against Harlequins on December 3.
England kick off their Six Nations campaign against Italy on February 4 and are bidding to become the first team to win the title three times on the trot.