Northampton Town can confirm that skipper Joseph Mills fractured his ankle in Saturday's draw at Crawley Town.
Mills suffered the injury in the second half and the fracture has been confirmed.
"It is really tough news for Millsy and the club and we will miss him," said manager Jon Brady.
"He is our captain and time and again he puts his body on the line for the club. Typical of him, it was a very brave tackle from him yesterday and unfortunately that is when he was injured.
"We wish him the speediest of recoveries and the club and our medical staff will work with him and offer him all the support we can to help him get back in the quickest possible time.
"He is a tough lad, not just physically but mentally too and knowing Millsy, he will be back declaring himself fit and available as soon as is humanly possible and we look forward to that happening.
"I am sure all supporters will join us all in wishing him well and we will support him in his recovery every step of the way."