Donald Philip Tregonning (born 26 November 1928) is a retired professional tennis player and coach.
Tregonning, a student of Melbourne coach Mick Sweetnam, was a member of the international professional tennis community, reaching the mixed doubles semi finals of the 1953 Australian Open, playing twice in the quarter finals of doubles competitions at the Australian Open (1949, 1953) and reaching the quarter finals of the Wembley Professional Championships in 1953.
Tregonning played in a famous 1953 Australian Open Round 1 match in which the umpire left the grounds to "go to (his) tea".
Tregonning is the former head-coach at Kooyong Lawn Tennis Club (the then site of the Australian Open), Danish national coach, French national coach (Davis Cup) and for 30 years he coached the Japanese national team and helped them to a 3-2 upset over Australia in the "Australian Davis Cup".
His clientele included Wimbledon finalist Kurt Nielsen, Grand Slam competitor Elizabeth Peers-Little, Australian Open doubles finalist Cliff Letcher, Grand Slam competitor Greg Whitecross and "Australian Junior" finalists Bill Durham, Trevor Little, Sally Irvine.