Brennan was pulled from Wednesday's game against Oakland after making a diving catch, Chris Assenheimer of the Elyria Chronicle-Telegram reports.
Brennan made a spectacular diving grab in right field during the fourth inning, but he landed awkwardly on his left arm and came up wincing. The Guardians will take a look at Brennan and should provide more updates shortly while Gabriel Arias replaces Brennan in the outfield.