John Ross Frederick Duncan (born 25 March 1944) is a former Australian cricketer who played one Test in 1971. A right-arm fast-medium bowler, Duncan was brought into the Test team for the Fifth Test at Melbourne which replaced the Victoria second tour match against the MCC in the 1970–71 Ashes series. Brought in as a fast-medium seam bowler to replace the injured Graham McKenzie, Duncan made only 3 with the bat and took 0/30 with the ball in the first innings, but did not bat or bowl in the second and took no catches. He was dropped for the Sixth Test in favour of Dennis Lillee. He also represented Australia in 1971–72 in one match against Gary Sobers' Rest of the World XI, again without success.