Thomas started in center field, batted eighth, and went 1-for-3 with a double and a run scored in Sunday's 4-0 win over the Rockies.
Thomas had his contract selected from Triple-A Reno and made his major-league debut. The plan is for him to start in center field for the time being while Daulton Varsho becomes the primary catcher with Carson Kelly (oblique) on the injured list, Nick Piecoro of the Arizona Republic reports. Kelly was diagnosed with a Grade 1 strain, the least severe, meaning the absence will not be prolonged. However the injury plays out, it's unlikely the Diamondbacks' plan is to promote Thomas for only a short period and thereby waste his MLB clock.