But that was not the-then 22-year-old southpaw's only problem.
During a sparring session in London before heading to the Netherlands, Morgan dislocated a knuckle on his left hand. The pain remained not only through the Games but for the rest of his life.
1928 was a big year for New Zealand boxing. Gisborne heavyweight Tom Heeney - dubbed the "Hard Rock from Downunder" - fought champion Gene Tunney in New York for the world title.
But Morgan made it a year to savour.
He was nothing if not determined in the Olympic ring. Having seen off Johannson with a second-round knockout, Morgan worked his way past a head-butting Italian, Romano Canova, on points, and Frenchman Rene Catalaud in his semifinal, also on points.
In the final he was up against experienced Argentine Raul Landini, who had the reputation of being a knockout puncher.
By this point Morgan couldn't even straighten his left hand but he outboxed Landini to win a unanimous points decision.
Morgan became New Zealand's first Olympic gold medallist (swimmer Malcolm Champion won gold as part of a 4 x 200m freestyle quartet representing Australasia in 1912).
Morgan had got himself a Games ticket by winning the national lightweight title in 1927, and in sufficiently impressive style to be named as part of a 10-strong New Zealand team for Amsterdam.
Morgan, who was born in London and educated at Wellington College, stood about 1.77m tall and weighed around 70kg. During his career he turned down approaches by British and American promoters, but eventually turned pro, with limited success.
In later life, Morgan ran a plumbing business in Wellington and remained involved in the sport as a referee.
He died in 1952, aged 46, of lung cancer, even though he was a non-smoker. He died as a result of inhalation of fumes while working as a plumber.
Morgan was inducted into the New Zealand Sports Hall of Fame in 1990.
