Kostjasyn suffered a throat injury follow accidental contact and was taken to hospital but was later discharged.
Kostjasyn is expected to be sidelined for a minimum of six to eight weeks.
Read the full press release by the Newcastle Knights below:
Kostjasyn was hospitalised however he has been discharged today (Monday).
The 29-year-old will be reassessed in four to six weeks to determine a return date to training. At this stage, Kostjasyn is expected to be out for a minimum of six to eight weeks.
The Club will continue to provide any further updates when appropriate.