Reed will be a non-roster invitee with the A's this spring.
He batted .228 with a career-high 14 home runs and 50 RBIs in 121 games for Double-A Amarillo last year. He walked a career-high 42 times for a .310 on-base percentage and ranked seventh in the Texas League with 23 stolen bases.
The 24-year-old right-handed hitter was rated as the Padres' 26th best prospect by ESPN's Keith Law before the 2019 season. He was a second-round pick in the 2016 draft and is a .249 career hitter with 33 home runs, 160 RBIs and 101 stolen bases in 382 games over four seasons as a professional.
The Associated Press contributed to this report.