Donald Philip Tregonning (born 26 November 1928) is a retired Australian professional tennis player and coach. For 30 years he coached the Japanese national team and helped it to a 3 - 2 upset over Australia in the "Australian Davis Cup". As a coach, his clientel included the "Australian Junior" champions Cliff Letcher and Greg Whitecross; the "Australian Junior" finalists Bill Durham, Trevor Little, Elizabeth Little and Sally Irvine and the Wimbledon finalist Kurt Nielsen.
Donald Philip Tregonning was born on 26 November 1928 in Melbourne, Victoria, Australia. In his childhood, he first played Australian Rules football and later discovered tennis as his passion. Tregonning received direct entry into the Men's Singles draw of the 1951 Wimbledon Championships but lost in the first round to Brazilian Armando Vieira. Tregonning partnered Peter Cawthorn in the Men's Doubles and reached the third round, including a first round win against Vieira and his partner Leon Norgarb. Tregonning returned to Wimbledon in 1952, but was defeated in the first round of the Men's Singles by Douglas Scharenguivel. He again partnered Cawthorn in the doubles event, but they were defeated in the first round by Americans Irvin Dorfman and Grant Golden. Upon his return to Australia Tregonning played in the Australian Championships and multiple State Championships. He played in the "World Professional Championships" in 1953. That same year, Tregonning traveled to England and coached and played there with Cawthorn for about 2 years. In 1955 he was appointed Danish national coach and prepared the tennis team for the Danish Davis Cup. In the same year he coached Kurt Nielsen, who reached the Wimbledon singles finals that year.
In 1956 Tregonning started coaching in Fawkner Park, Melbourne. In February 1956 he and five others founded the Professional Tennis Association of Victoria, which later changed its name to the Tennis Coaches Association of Victoria (TCAV) in 1973. In 2010 Tregonning was inducted into the TCAV Hall of Fame with "Legend" status in recognition of his service to the organisation for more than forty years.