Thomas was placed on the 7-day injured list at Triple-A Reno on Tuesday with a right oblique strain, Jesse Friedman of GoPHNX.com reports.
After losing work in the majors to Jake McCarthy, Thomas was optioned to Triple-A last week in order for him to continue receiving regular reps. However, he is now expected to be sidelined for roughly four weeks as a result of his injury. The 24-year-old outfielder had gone 5-for-13 with a homer and two RBI in three games with the Aces.