The risk of bleeding into a joint following a local injection if you are on warfarin is very small if your warfarin dose and warfarin blood tests are stable (INR less than three) and there is usually no need to discontinue warfarin prior to the injection.
If you are on tablets such as Xarelto® (rivaroxaban), Pradaxa® (dabigatran), or Eliquis® (apixaban) or similar for an irregular heart beat (atrial fibrillation), we would advise you to leave at least 24 hours between the last tablet and the injection, to minimise the risk of bleeding into the joint.