A post-mortem examination has revealed that the Radcliffe schoolboy died of a blood clot.
His father Stephen Platt wants to make people aware of the symptoms his son experienced to try and prevent similar deaths, after receiving the post-mortem findings last Thursday.
The 48-year-old, who lives in Cobden Street, Radcliffe, said: "We were told it is very rare for someone so young to die of a blood clot. It went straight up his leg to his heart and caused a cardiac arrest.
"I was devastated. If Lewis had had a couple of aspirin the blood clot would not have formed and killed him.
The post-mortem report found St Gabriel’s RC High School pupil Lewis had died of pulmonary embolism, a blocked artery in the lungs due to a blood clot that had moved from elsewhere in the body.
Aspirin therapy can reduce the clumping action of blood platelets — possibly preventing a heart attack.
The post-mortem also found that Lewis had hepatomegaly, an abnormal enlargement of the liver, which can cause liver disease if a person is overweight.
Mr Platt said: "If a child is becoming obese you need to be careful as you can't see the damage it's doing inside your body. Lewis was always playing football with me or on his bike or scooter but even an active child can have health problems as his death has shown."
Two days before his death, Lewis had been to the doctor because his feet had swollen up, and was given antibiotics.
On Wednesday, March 7, dad and son had gone for a drive in their new car, but as they returned home Mr Platt could tell Lewis was not feeling himself.
Mr Platt said: "Lewis said he was alright one minute. Then he was gone.
"I was on my hands and knees giving him mouth to mouth for 20 minutes.
"We thought we would give the antibiotics some time to kick in. The doctor had asked us to revisit on Thursday.
"If you get a blood clot at 50 or 60 it is worrying. People don't think this can happen when you are young."
Mr Platt urged families to take their children for an X-ray if they complain of sore legs or swollen feet.
A football-themed headstone is currently being designed for Bury FC supporter Lewis.
Mr Platt also hopes to run the Greater Manchester Marathon next year in Lewis's honour.
He said: "We were stuck together like glue. We went everywhere together. He was by my side for 13 special years."