"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," said Lancaster.
"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."
Croft, who celebrated his 100th appearance for Leicester in last weekend's big win over sale Sharks, is one of 36 players who will meet up at Pennyhill Park as England prepare for their round four clash with Italy at Twickenham. Alex Corbisiero (London Irish), Owen Farrell (Saracens) and Ben Morgan (Gloucester Rugby) will continue their recovery in camp, but won't figure in selection.
Croft was one of the stars of the 2009 British & Irish Lions Test pack after joining the tour as a last minute replacement for Alan Quinlan. He scored two tries in the first Test and then figured in the rest of the series at blindside flanker.
"England would be a bonus after the season I have had," said Croft. "My first priority is playing for Leicester and helping the club win silverware, and if that led to selection for the summer tour, that would be good."
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)