Sammie Szmodics (Bristol City), Josh Knight (Leicester City) and Reece Brown (Huddersfield) all excelled in Posh colours during the 2019-20 season.
Posh director of football Barry Fry said: “We had a conversation with all of them about coming back in some way next season, but for now they all wanted to return to their former clubs and have a go at getting a game for them.
“Good luck to them. They were all good for us and maybe we will look again if things don’t work out as they expect.”
Szmodics used social media to say: “Unfortunately my time at Posh has come to an end. I enjoyed my short time at the club. Thanks to the gaffer, players, staff and fans for making me feel loved. All the best for the future.”
And Knight, who also played for Posh on loan in the 2018-19 campaign, also said goodbye on Twitter.
He said: “ I just wanted to say a massive thank you to the staff, players and the fans for making me feel so welcome again this season. I am truly disappointed on how the season finished. I’d like to wish the club the very best for the future.”