Sportal.co.nz 17.Sep.2013Getty Images
Croft, who toured with the British and Irish Lions to Australia, suffered knee ligament damage while playing for his Leicester club and he has been ruled out for the season.
England are set to play Australia, Argentina and New Zealand in November and will face a big job to find a replacement.
Forwards coach Graham Rowntree told SportingLife.com: "Tom Croft is a huge loss, he's desperately unlucky.
"To come back from a broken neck, play for England and be part of a winning Lions series, only to then get injured again and miss another season...I'm gutted for him.
"I really feel for him because he was outstanding in the Lions series. He made a huge impact on that tour and is a special player.
"He has points of difference to his game and will be missed by England and Leicester," he said.
Chris Robshaw and Tom Wood are leading candidates to replace him while other players were emerging from the England Lions tour of Argentina.
Rowntree said England's players had learned plenty from the Lions tour to Australia.
"Off the field they experienced how diligent the other nations are in terms of doing their homework and knowing their roles because on a Lions tour you don't have so much time to do things.
"Senior pros such as Brian O'Driscoll, Paul O'Connell and Alun Wyn Jones were very good at that. They picked up a lot of training from those guys," he said.