Cocaine abuse is a Substance Use Disorder. It is a disorder of choice and cannot arise from injury.
Bottomline _ You have NO responsibility for a patient_s non-prescription drug abuse.
Also, cocaine use is rarely a single event. If he/she is willing to become involved with A.A. and N.A. as well as enter a drug rehab program, he may begin the process of recovery. Again, this is not your responsibility; it is solely that of patient and family.
Does he have problems with the work environment (e.g. PTSD or similar anxiety disorder)? If he is released to the exact environment in which he was traumatized, you may potentiate the psychological symptoms. You need to avoid this.
Thus, if he returns to work, it should likely be in a setting that differs from the one (machinery, heights, closed space, etc) in which he was injured.
One final point: if the employer has a zero tolerance drug policy, all of this is moot. Even if he is capable, the employer may fire him.