From a medical standpoint this is true, but whether or not a hockey organization will respect that is another issue.
Exactly how long depends on the severity the concussion, anywhere from weeks to months. The assesment factor is symptoms with the period being defined as: time while symptomatic + 1 month symptom free before returning to any contact sports. Anything less than that, and you risk permanent brain damage (if it hasnt already occured). Look at Primeau....
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Avandia Lawyer