International newcomer Max Evans joins his brother Thom in the squad, while fellow Glasgow team-mates Moray Low, Dan Turner and Mark McMillan are all given a chance to impress Hadden for the first time. Newcastle fly-half Stephen Jones and Edinburgh's Geoff Cross and Calum McRae are also afforded the same opportunity.
Northampton Saints wing Sean Lamont, who made plenty of headlines when he burst on to the international scene in 2004, returns to the squad after missing the whole of the 2008 Six Nations with a knee injury.
Previous Lions tourists Chris Cusiter, Simon Taylor and Jason White are also included.
"The purpose of this squad session is really two-fold; firstly to debrief following the Argentina tour; and secondly for the players to be introduced to our new two assistant coaches, Mike Brewer and Graham Steadman, ahead of our assembly for the autumn Tests in November," said Hadden, who made the changes to his coaching set up earlier this year.
Scotland squad for September 22 training session
Backs - Mike Blair (Edinburgh), Ben Cairns (Edinburgh), Chris Cusiter (Perpignan), Simon Danielli (Ulster), Nick De Luca (Edinburgh), Rob Dewey (Ulster), Max Evans (Glasgow), Thom Evans (Glasgow), Phil Godman (Edinburgh), Andrew Henderson (Glasgow), Stephen Jones (Newcastle), Rory Lamont (Sale), Sean Lamont (Northampton), Rory Lawson (Gloucester), Calum MacRae (Edinburgh), Mark McMillan (Glasgow), Graeme Morrison (Glasgow), Dan Parks (Glasgow), Chris Paterson (Edinburgh), Gordon Ross (Saracens), Hugo Southwell (Edinburgh), Nikki Walker (Ospreys), Simon Webster (Edinburgh)
Forwards - John Barclay (Glasgow), Johnnie Beattie (Glasgow), Kelly Brown (Glasgow), Dave Callam (Edinburgh), Geoff Cross (Edinburgh), Alasdair Dickinson (Gloucester), Ross Ford (Edinburgh), Dougie Hall (Glasgow), Craig Hamilton (Edinburgh), Jim Hamilton (Edinburgh), Nathan Hines (Perpignan), Allister Hogg (Edinburgh), Allan Jacobsen (Edinburgh), Alastair Kellock (Glasgow), Gavin Kerr (Edinburgh), Scott Lawson (Gloucester), Moray Low (Glasgow), Scott MacLeod (Scarlets), Euan Murray (Northampton), Scott Murray (Montauban), Matt Mustchin (Edinburgh), Ross Rennie (Edinburgh), Alasdair Strokosch (Gloucester), Simon Taylor (Stade Francais), Fergus Thomson (Glasgow), Dan Turner (Glasgow), Jason White (Sale)
Scotland's autumn fixtures
November 8 - New Zealand
November 15 - South Africa
November 22 - Canada