Cardinals manager Oli Marmol confirmed Wednesday that Walker will be in the Opening Day lineup Thursday against the Blue Jays, Katie Woo of The Athletic reports.

Marmol's announcement comes as no surprise after the 20-year-old top prospect was informed Saturday he had made the 26-man major-league roster. Walker will start in one corner-outfield spot Thursday, with Lars Nootbaar covering the other. Tyler O'Neill or Dylan Carlson will patrol center field.