Central defender Aaron Downes has agreed to sign a new two year deal in the summer that will see the 23 year old staying with the Spireites until June 2011.
The club had made the offer of a new contract before the young Australian suffered a serious knee injury in the Easter weekend game at home to Darlington, which sees him sidelined from six to nine months, and were keen to reassure him that the club would continue to honour the deal.
Chesterfield manager Lee Richardson said: "Aaron has been in great form this season and I am delighted that the club has moved quickly to reassure him that his future is with the Spireites."
Downes suffered anterior cruciate ligament damage and is to have an operation, which will be followed by a lengthy period of rehabilitation.
Lee Richardson added: "He is a fit young lad and there is every expectation that he will fully recover."