Peterborough have transfer-listed 11 players, including midfielders Michael Bostwick and Marcus Maddison.
Both have 12 months to run on their contracts and Posh routinely make all such players available.
Lee Angol, Jordan Nicholson, Jerome Binnom-Williams, Hayden White and Luke James also fall under that category.
However, forwards Adil Nabi and Shaquile Coulthirst, midfielder Brad Inman and defender Michael Smith have all been told to find new clubs.
Loanees Craig Mackail-Smith and Luke McGee have returned to their parent clubs.
Bostwick has made 228 appearances for Posh since his 2012 move from Stevenage, while boss Grant McCann recently described Maddison as "on his day, one of the best in this league, if not the best".
However, both could be sold if they do not agree new deals, with Peterborough reluctant to allow them to leave for free.
'Mediocrity doesn't sit with me'
After the season-ending defeat at Bolton on Sunday, McCann threatened major changes to his squad after they finished 11th in League One.
"There'll be quite a few going on the transfer list," he told BBC Radio Cambridgeshire.
"I think we need to make it very clear now that mediocrity doesn't sit with me very nicely.
"I'm disappointed, when probably I shouldn't be in my first year as a manager, to finish where we are in the league.
"I'm a born winner. I thought I had the right people in the changing room - obviously I didn't. But I definitely will next year.
"[We need] people who have got that bit more drive and determination. We haven't had it and it's definitely something we need to have a look at."