Injury has meant Flood has made just substitute appearance against Wales, while Youngs has lost his starting spot to Northampton's Lee Dickson.
The duo are both likely to start the Tigers' Aviva Premiership clash with Gloucester as they look to press their claims for a return to the England first XV against France.
Ben Morgan is the only member of the starting XV from the defeat to the Welsh to be back with his club this weekend, with International Rugby Board regulations forcing interim head coach Stuart Lancaster to allow the No8 to play for the Scarlets in Friday's RaboDirect PRO12 tie with Connacht.
Former Lions tourists Lee Mears, Charlie Hodgson and Matt Stevens are also among those released, as is Northampton second row Courtney Lawes.
"We are going to release 18 players to get some game time for their clubs on which should be a very competitive weekend. Our intention was to retain the starting 15 from Wales for training tomorrow but under IRB Regulation 9 Scarlets haves a requested Ben Morgan so he will be returning to play for them on Friday," said Lancaster.
"We're not obliged to release any other players back. From my point of view we want the boys to go back and play. In order to play international rugby you've got to be in form, you've got to be playing well and to do that you've got to be playing rugby.
"Clearly there are selection decisions going into the game against France - and there are now 18 players going back to their clubs - so we might have some other selection decisions to make on the back of what happens this weekend."
The 14 remaining members of England's 6 Nations training squad will continue to train at Loughborough University today and will the meet up at Pennyhill Park on Monday evening.
Mike Brown (Harlequins)
Calum Clark (Northampton Saints)
Paul Doran Jones (Northampton Saints)
Phil Dowson (Northampton Saints)
Toby Flood (Leicester Tigers)
Charlie Hodgson (Saracens)
Courtney Lawes (Northampton Saints)
Joe Marler (Harlequins)
Lee Mears (Bath Rugby)
Ben Morgan (Scarlets)
Tom Palmer (Stade Francais)
Charlie Sharples (Gloucester Rugby)
Joe Simpson (London Wasps)
Matt Stevens (Saracens)
Jordan Turner-Hall (Harlequins)
Thomas Waldrom (Leicester Tigers)
Rob Webber (London Wasps)
Ben Youngs (Leicester Tigers)