In 12 games with Memphis, the muscular Canadian batted .388 with six homers, 18 RBIs and an .837 slugging percentage. The sizzling start came after he pulled a hamstring during spring training.
O'Neill gives the Cardinals another position player while outfielder Tommy Pham rests a groin injury.
Manager Mike Matheny said he "wouldn't hesitate to throw Tyler in just about any spot in the outfield and get him an at-bat in a big situation."
The Associated Press contributed to this report.