Frecklington has made 16 appearances for the Millers, scoring four goals, since arriving on loan in October and the two clubs are currently thrashing out a permanent deal for the 27-year-old.
"The chairman (Tony Stewart) and (Peterborough director of football) Barry Fry are two of the best negotiators you could wish to meet," manager Steve Evans told the club's official website.
"Approaching Christmas, one day I was confident, the next not so much, but now I think things are looking good."
"It's not (done). There's terms to be agreed by Lee once the fee is set in stone, but it's not right to do that until the terms with the club are sealed."
Evans added: "He's been down in recent weeks, his performances haven't quite been there, but he's a young lad pondering his future and I love him to bits so we'll get him back on top of his game."