Back has recently become Leicester's assistant coach

Two other World Cup squad members, Kyran Bracken and Martin Corry, plus Graham Rowntree, have also been left out of the 28-man group.

"It's always hard to leave out such established international players as Back, Bracken, Corry and Rowntree," said England coach Sir Clive Woodward.

"But as always I am looking at current form and will continue to do so."

Woodward will whittle down the 28 players to a match squad of 22 on Monday, who will then travel to Rome.

I don't want to give up on playing for England Neil Back, earlier this week

The omission of Back will inevitably lead to suggestions that his 66-cap Test career could be over.

The 35-year-old recently put his name forward as a possible captaincy successor to the retired Martin Johnson, before Lawrence Dallaglio took over.

But Back has subsequently taken on a coaching role with Leicester in the wake of Dean Richards' departure as director of rugby.

Only this week though, when he handed the Tigers captaincy back to Johnson, Back expressed a desire to continue playing for England.

"With the Six Nations coming up, hopefully I'll have a heavy involvement in that," he said.

Thompson doubt for England

"The desire is still there to play a big part in the national squad, so I don't want to give up on playing for England."

Back's absence, along with Corry and the injured Lewis Moody and Alex Sanderson, leaves England with only three specialist back-row players in the squad.

Richard Hill is set to revert to his old openside role, with Wasps' Joe Worsley a likely starter in the back row.

It really is the end of a glorious era, the start of another one From Tim Hague Have your say on Scrum V

Sale's athletic lock Chris Jones can also play at number eight, while Gloucester duo Andy Hazell and James Forrester are among eight younger players who will take part in training this week.

Bracken has failed to find top form for Saracens since returning from the World Cup.

His omission leaves the scrum-half berth a straight fight between Matt Dawson, who returned to action for Northampton on Saturday, and Gloucester's Andy Gomarsall.

England training squad:

Backs: I Balshaw (Bath), B Cohen (Northampton), J Lewsey (Wasps), J Robinson (Sale), J Simpson-Daniel (Gloucester); W Greenwood (Harlequins), H Paul (Gloucester), O Smith (Leicester), O Barkley (Bath), P Grayson (Northampton), A King (Wasps), M Dawson (Northampton), A Gomarsall (Gloucester).

Forwards: M Regan (Leeds), S Thompson (Northampton), D West (Leicester); J Leonard (Harlequins), M Stevens (Bath), P Vickery (Gloucester, vice captain), T Woodman (Gloucester), S Borthwick (Bath), D Grewcock (Bath), C Jones (Sale), B Kay (Leicester), S Shaw (Wasps), L Dallaglio (Wasps, captain), R Hill (Saracens), J Worsley (Wasps).

Young players to train with England squad:
D Scarbrough (Leeds), P Christophers (Leeds), H Ellis (Leicester), ATitterrell (Sale), D Flatman (Bath), T Palmer (Leeds), A Hazell (Gloucester), J Forrester (Gloucester).