Johnathan Keith Gainer
- Bats Left, Throws Left
- Height 6' 0", Weight 190 lb.
- School University of South Alabama
- High School Rutherford High School (Panama City)
- Debut May 14, 1993
- Final Game October 2, 1993
- Born October 8, 1966 in Panama City, FL USA
First baseman Jay Gainer was signed by scout Hosken Powell for the San Diego Padres as a 24th round pick in the 1990 amateur draft. In his professional debut, 1990 with the Spokane Indians, he led the Northwest League in hitting (.365) and tied for the league lead with 21 doubles. His 10 home runs and 54 RBI placed him second to teammate and league MVP Matt Mieske (12 and 63, respectively).