John Gustaf Lager (1 March 1887 – 17 February 1961) was a Swedish rower who competed in the 1912 Summer Olympics and in the 1920 Summer Olympics.
In 1912 he was a member of the Swedish boat Vaxholm which was eliminated in the first round of the coxed four competition.
Eight years later he was part of the Swedish boat which was eliminated in the first round of the coxed four event.