Leicester Tigers back-rower Croft is among 36 players to meet up at Pennyhill Park after his succeasful recovery from a serious neck injury.
Croft captained Tigers to victory over Sale Sharks at Welford Road on Saturday in his fifth appearance of the season and his 100th start for the club.
He takes the Tigers representation in the England squad up to eight with Tom and Ben Youngs, Dan Cole, Geoff Parling, Thomas Waldrom, Toby Flood and Manu Tuilagi also involved.
England head coach Stuart Lancaster said: “The indications last week were that it might be a bit early for Tom to get involved in this Six Nations. But, having played back-to-back games, he has now had the all-clear from the specialist, and Leicester’s and our medics.
“I also had a good chat with Richard Cockerill – he is happy with his form and we can clearly see he is playing well. But most importantly Tom feels he is ready. It is great to have him back in.
“We have competition in all places but the back row is very competitive and to have Tom available just adds to that so we are looking forward to seeing how he does this week. We are also bringing in Calum Clark as we want to keep supporting him and involved during his recovery (from a shoulder injury).”
Alex Corbisiero, Owen Farrell and Ben Morgan will also continue their recovery in camp.
England training squad
Chris Ashton (Saracens)
Brad Barritt (Saracens)
Mouritz Botha (Saracens)
Mike Brown (Harlequins)
Freddie Burns (Gloucester Rugby)
Danny Care (Harlequins)
Calum Clark (Northampton Saints)
Dan Cole (Leicester Tigers)
Tom Croft (Leicester Tigers)
Lee Dickson (Northampton Saints)
Alex Corbisiero (London Irish)
Owen Farrell (Saracens)
Toby Flood (Leicester Tigers)
Ben Foden (Northampton Saints)
Alex Goode (Saracens)
Dylan Hartley (Northampton Saints)
James Haskell (London Wasps)
Matt Kvesic (Worcester Warriors)
Joe Launchbury (London Wasps)
Courtney Lawes (Northampton Saints)
Joe Marler (Harlequins)
Ben Morgan (Gloucester Rugby)
Geoff Parling (Leicester Tigers)
Chris Robshaw (Harlequins)
David Strettle (Saracens)
Henry Thomas (Sale Sharks)
Joel Tomkins (Saracens)
Manusamoa Tuilagi (Leicester Tigers)
Billy Twelvetrees (Gloucester Rugby)
Mako Vunipola (Saracens)
Billy Vunipola (London Wasps)
David Wilson (Bath Rugby)
Thomas Waldrom (Leicester Tigers)
Tom Wood (Northampton Saints)
Ben Youngs (Leicester Tigers)
Tom Youngs (Leicester Tigers)