The Cubs recalled Ferguson from Triple-A Iowa on Tuesday, Vinnie Duber of the Chicago Sun-Times reports.
Ferguson will be summoned back to the big leagues to fill in for Trent Thornton while the latter is out on paternity leave. Ferguson gave up four earned runs in 1.1 innings during his lone MLB outing of the season with the A's, though he owns a 2.79 ERA and 1.20 WHIP at Triple-A since joining the Cubs organization.