All three played a key role in England's credible second-place finish in the 2012 RBS 6 Nations.
Leicester duo Croft and Youngs have neck and knee problems respectively, while London Irish loosehead Corbisiero continues his rehabilitation from knee surgery.
Leicester director of rugby Richard Cockerill was wary with his assessment of the flanker and scrum-half.
He said on Wednesday: "They are doing well but it will be two months," news which will no doubt concern Lancaster.
Brian Smith, director of rugby at London Irish, was equally cautious on Corbisiero, who hasn't played since sustaining his knee injury on England's summer tour to South Africa.
The latest setback for Youngs, 22, comes after he injured his shoulder against the Springboks on the same tour, and prevented him from playing in Leicester's season opener against London Welsh last Sunday.
The England set-up had hoped Youngs would return in mid-October, but this now seems unlikely.
Croft has been on the sidelines since injuring his neck against Harlequins in a Premiership match at the Stoop in April.
However, there is brighter news for the Northampton's 23-year-old Courtney Lawes. Director of rugby Jim Mallinder said: "He is a few weeks away," as the lock continues his recovery from elbow surgery after a pre-season injury.
Lawes was absent from England's RBS 6 Nations campaign earlier this year through a shin injury which also kept him out of the South African tour.