The teenager who was a pupil at St. Michael's College in Enniskillen, Co Fermanagh was injured during a football match on Monday.
Oisin, a keen footballer, was being treated for his injuries in the Royal Victoria Hospital in Belfast.
First Minister Peter Robinson commented on the tragic incident, saying: "Young Oisin Mc Grath's death is heartbreaking. I'll be praying for his family and all those devastated by this sad news tonight."
It is understood that Oisin was showing no signs of life while under medical care and it was decided that artificial support would be gradually removed.
It has been reported that a 17-year-old youth was arrested regarding the incident, but was bailed pending further police inquiries.
Oisin was described as "happy, helpful and intelligent."
Our thoughts go out to Oisin's family and friends at this devastating time.
