Northampton's Robbie Kydd, who can play at full-back or centre, is joined by Border Reivers full-back Calum MacRae, Edinburgh prop Alasdair Dickinson and Glasgow flanker John Barclay.

Hadden has named a 33-man squad for the get-together, which takes place next Monday and Tuesday.

Wingers Simon Danielli, Rory Lamont and Nikki Walker are also selected, reinstated after missing the November Tests.

Hadden is eager to explore all his options ahead of the much anticipated opening Calcutta Cup clash against England at Twickenham.

"I'm very pleased with the competition for places on the wing and in our back three in general," said Hadden.

"We've some top-class options available to us there when you consider Sean Lamont, Simon Webster, Hugo Southwell and Chris Paterson were all in that selection mix during the November Tests.

"Now Rory and Simon are coming back from injury and along with Nikki all are going extremely well and have justified their call-up.

An array of injuries mean Scotland are likely to be weakened for the Twickenham clash, but Hadden is determined to keep the team spirit going.

Consequently he has also invited eight injured players to the sessions, including Edinburgh's Mike Blair who suffered shoulder damage against Llanelli last Friday which could side-line him for eight weeks.

Rob Dewey is not listed among the injured, supporting Edinburgh's claim that their centre should be fit to train next week.

Dewey sustained a knee ligament injury in Scotland's victory over Romania in November but has made a good recovery.

"Though the injury list is extensive, Jason White is currently our only player who we would describe as long-term injured," Hadden said.

Scotland training squad:

Backs: Simon Danielli (Border Reivers), Rob Dewey, Marcus Di Rollo and Phil Godman (all Edinburgh Rugby), Andrew Henderson (Glasgow Warriors), Robbie Kydd (Northampton Saints), Rory Lamont (Glasgow Warriors), Sean Lamont (Northampton), Rory Lawson (Gloucester), Calum MacRae (Border Reivers), Dan Parks (Glasgow Warriors), Chris Paterson (Edinburgh Rugby), Sam Pinder (Glasgow Warriors), Hugo Southwell (Edinburgh Rugby), Nikki Walker (Neath Swansea Ospreys).

Forwards: John Barclay (Glasgow Warriors), Johnnie Beattie (Glasgow Warriors), Kelly Brown (Border Reivers), David Callam (Edinburgh Rugby), Alasdair Dickinson (Edinburgh Rugby), Bruce Douglas (Border Reivers), Ross Ford (Border Reivers), Dougie Hall (Edinburgh Rugby), James Hamilton (Leicester), Allan Jacobsen (Edinburgh Rugby), Alastair Kellock (Glasgow Warriors), Gavin Kerr (Border Reivers), Scott MacLeod (Llanelli Scarlets), Donnie Macfadyen (Glasgow Warriors), Scott Murray (Edinburgh Rugby), Euan Murray (Glasgow Warriors), Alasdair Strokosch (Edinburgh Rugby), Simon Taylor (Edinburgh Rugby)

Injured but invited to attend: Mike Blair (Edinburgh - shoulder), Chris Cusiter (Border Reivers - shoulder), Nathan Hines (Perpignan - foot), Allister Hogg (Edinburgh - knee), Scott Lawson (Glasgow - foot), Ben MacDougall (Border Reivers - cheekbone), Simon Webster (Edinburgh - lower leg), Jason White (Sale Sharks - knee).