Single-A Hill City placed Oakie on its 7-day injured list Wednesday due to a viral illness.
Oakie hadn't pitched for Hill City since June 24 before the club deactivated him two weeks later. The young righty is regarded as one of the Guardians' better lower-level pitching prospects but has struggled to a 7.15 ERA, 1.95 WHIP and 56:42 K:BB over 45.1 innings with Hill City this season.