Louis Reed, who spent last season on loan to the Spireites from Sheffield United, has joined Peterborough United.
Posh confirmed the purchase of the 20-year-old on Monday for an undisclosed fee.
He’s signed a three-year deal with Steve Evans’ side.
The Scot tried to take Reed to Mansfield on loan last summer before he joined Town during their pre-season tour in Spain and Portugal and became a key player in the heart of the midfield.
He played 47 of the Spireites’ 52 matches, scored four goals and made the most passes last season of all League Two players.