Mclean has said he wants to leave London Road after being dropped for Posh's game with Newcastle in November.
"I did not hand in a request at the time as the chairman asked me to back him but I can't get over the way I was treated," he told the club's website.
"I was made club captain and dropped for the biggest game of my career.
I now feel these factors, my age and my family commitments make it the right time to move clubs Peterborough striker Aaron Mclean "After the game I spoke with the chairman about how upset I was. I decided to try and get on with things as the chairman, staff and supporters have been very dear to my heart.
"But I now feel these factors, my age and my family commitments make it the right time to move clubs."
Mclean joined Posh from Grays for £150,000 in January 2007 after a two-month loan spell at London Road.
He has made 144 appearances for Peterborough, scoring 68 goals.