Also non-tendered were pitcher Jairo Cuevas and infielder Jason Smith, who was designated for assignment earlier in the day.
All four players become free agents and can sign with any club, including the Royals. All except Cuevas were eligible for salary arbitration.
Bale, who made $2.2 million last season, began the year in the rotation but made just three starts before being stopped by shoulder fatigue. While rehabbing, he broke his left pitching hand while punching a door in apparent frustration about his progress. But he came back strong in September, not allowing a run in 10 relief appearances.
The Royals have talked this winter of using Bale in the bullpen, an indication that they might try to re-sign him.
Gathright, a speedy reserve outfielder, hit .254 in 105 games and had 21 stolen bases in 25 attempts. His future with the Royals was clouded after the team obtained center fielder Coco Crisp from the Boston Red Sox.
Cuevas, seen as a power starting right-hander, is recovering from shoulder surgery and might not be able to pitch until July or August, if then. He's gone from the Braves to the Royals, back to the Braves, then back to the Royals -- all in waiver transactions this winter.
Smith played little for the Royals but hit 20 homers for Triple-A Omaha and was a Pacific Coast League All-Star.
The moves leave the Royals' roster at 37.
Dick Kaegel is an executive editor for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.