The injury will require surgery and will see Maynard our for a number of months.
It's a cruel blow to both player and club.
Cardiff City's head of performance Richard Collinge said: "He will remain under the care of a local orthopaedic specialist and the Cardiff City medical team, working through a substantial rehabilitation programme with the goal of returning to first team action when possible.
"Instances such as this can see varied recovery times and we will do everything to support and guide Nicky through the rehabilitation process.
"The player has the backing of all of us at the club and we all wish him a speedy recovery, coming back stronger than ever."
After setting up goals for City v Wolves and Leeds and causing opposition defences problems with his pace and movement he will be missed.
Get well soon.