Scans have confirmed that David Mundy has sustained a fibular fracture above his left ankle.
The fracture will require non weight-bearing immobilisation for at least four weeks.
General manager of football Peter Bell said it was a disappointing setback for the veteran midfielder.
“Most likely, the fracture is a result of an injury that David sustained whilst riding his bike with his children,” Bell said.
“Post the incident, David completed two weeks of training without any issue, but presented with soreness last Friday.
“David is a professional and we are sure he will do everything he can to get his body in the best shape for 2020.
“Given the type of injury, at this stage there are no set time frames for David’s return to football.”