The Athletics selected Estes' contract from Triple-A Las Vegas on Wednesday, Martin Gallegos of MLB.com reports.
Estes is set to make his major-league debut Wednesday with a start in Oakland against the Mariners. The right-hander has collected a 3.74 ERA, 1.16 WHIP and 131:43 K:BB over 137 innings between Double-A Midland and Las Vegas this season. Estes is a nice prospect but isn't a great streaming option for his debut.