| Tuppy Diack | |
| Birth Name: | Ernest Sinclair Diack |
| Birth Date: | 22 July 1930 |
| Birth Place: | Invercargill, New Zealand |
| Ru Position: | Wing |
| Repteam1: | NZ Universities |
| Repyears1: | 1955–60 |
| Repyears2: | 1959 |
| Repcaps1: | 18 |
| Repcaps2: | 1 |
| Reppoints2: | 0 |
| Province1: | Otago |
| Province2: | Southland |
| Provinceyears1: | 1951–53, 55–64 |
| Provinceyears2: | 1954 |
| Provinceapps1: | 101 |
| Provinceapps2: | 7 |
| School: | Gore High School |
Ernest Sinclair "Tuppy" Diack (born 22 July 1930) is a former New Zealand rugby union player. A wing three-quarter, Diack represented Otago and, briefly, Southland at a provincial level. He played one match for the New Zealand national side, the All Blacks, namely the second test against the touring 1959 British Lions.[1]