Spence was placed on the 7-day injured list Monday at Triple-A Omaha due to an unspecified injury.
The 28-year-old righty's move to the IL represents yet another hit to the Royals' starting pitching depth, as the organization has already lost Cole Ragans, Stephen Kolek, Luinder Avila, Ryan Bergert and Alec Marsh to season-ending surgeries. Spence has been part of the Royals' 40-man roster all year, logging a 5.35 ERA and 1.41 WHIP over 16 starts with Omaha and yielding 22 earned runs in 9.1 innings over three appearances at the big-league level.