| John Greenig | |
| Position: | Pitcher |
| Bats: | Unknown |
| Throws: | Right |
| Birth Date: | c. 1848 |
| Birth Place: | Philadelphia, Pennsylvania, U.S. |
| Death Place: | Philadelphia, Pennsylvania, U.S. |
| Debutleague: | MLB |
| Debutdate: | May 9 |
| Debutyear: | 1888 |
| Debutteam: | Washington Nationals |
| Finalleague: | MLB |
| Finaldate: | May 9 |
| Finalyear: | 1888 |
| Finalteam: | Washington Nationals |
| Statleague: | MLB |
| Stat1label: | Win–loss record |
| Stat1value: | 0-1 |
| Stat2label: | Earned run average |
| Stat2value: | 11.00 |
| Stat3label: | Strikeouts |
| Stat3value: | 2 |
| Teams: | |
John A. Greenig (c. 1848 – July 28, 1913) was an American professional baseball player who played pitcher in the Major Leagues for the Washington Nationals of the National League on May 9, 1888.