The sole exception occurred in the 1984 Summer Olympics in Los Angeles, when Gross was one of the great athletes of the games. Gross easily won gold in the 200 m freestyle, dominating the field. In the 100 m butterfly, Gross pulled off a bit of an upset, winning over the favorite in the event, American Pablo Morales. However, in the 200 m butterfly, Gross himself was upset by a relative unknown, Australian Jon Sieben. The men's 4x200 m freestyle relay race became one of the marquee events of the games, with Gross leading the German relay against the underdog American squad. Despite the fact that Gross swam the fastest relay leg in the event's history, the American team pulled off the upset, earning the title of the Grossbusters.
Gross won a total of thirteen medals at the World Championships (including five gold), fifteen gold medals at the European Championships and was elected German "Athlete of the Year" four times (1982, 1983, 1984 and 1988). He retired from professional swimming in 1991.
1976 gold medal winning swimmer John Naber remarked to Sports Illustrated in 1984 that if Michael Gross were an American, he would have won six or seven medals, and that Gross was better than Mark Spitz.