In the summer of 1974, McGrain was diagnosed as suffering from diabetes. He had just returned home from playing for Scotland in the World Cup in West Germany, where he had displayed an excessive thirst and lost 2 stones (12 kg) in weight. Despite his condition, McGrain was able to continue playing top-level football. In March 2002 McGrain was found by police in the south side of Glasgow, slumped unconscious in the driver's seat of his car. He had entered a hypoglycaemic state, where the brain is drained of sugar and causes the body to shut down to conserve what little there is left. The officers revived McGrain and fed him a sugary sweet. Had McGrain not been found in time he would have suffered brain damage and possibly died. However, he made a full recovery and commented "There was no harm done in the end."