League One rivals Wycombe Wanderers have re-signed their former winger Fred Onyedinma after his release from Luton Town and Leyton Orient have signed former Posh loanee defender Dominic Ball after his release by Ipswich Town.
EFL clubs can sign free agents outside of transfer windows and Huddersfield Town snapped up striker Freddie Ladapo who was also released by Ipswich.
League One clubs have to register their squads with the EFL early in September.
Clubs are allowed a maximum of 22 outfield players of which eight have to be homegrown. Homegrown to the EFL means a player, regardless of their nationality, who has been trained by their club or by another club in the same national association for at least three years between the ages of 15 and 21.
In all three EFL divisiona, clubs have to name at least seven homegrown players among their matchday squad for any one game.
Clubs also need to name at least one club developed player in their matchday squad. A club developed player is one who has been registered with the club for at least 12 months before the end of their Under 19 season
Posh have lodged a 20-man squad list with the EFL, plus a list of 14 under 21 contracted players.
Transfer-listed players Romoney Crichlow and David Ajiboye are on the former list as are teenagers Sam Curtis and James Dornelly, plus goalkeepers Nicholas Bilokapic and Jed Steer.
Fourteen of the 20 players qualify as homegrown. Swedish striker Gustav Lindgren will be added to the list when he becomes eligible to play in January.
First-team squad regulars Malik Mothersille, Cian Hayes and Dion O’Brien-Brady are on the under 21 list as are summer signing George Nevett and deadline day capture Bradley Ihionvien.