As noted in the recap to Saturday's loss, Luis Valbuena was unavailable to pinch-hit due to an oblique strain that has now put him on the 15-day disabled list. (It also meant that the Cubs were, effectively, playing with a 23-man roster Saturday, as Donnie Murphy had not arrived in time for the game. But that's another story.)
Sunday, the Cubs will presumably have Murphy and another recall from Iowa:
Watkins was the Cubs' Minor League Player of the Year in 2012 when he hit .281/.383/.422 for Double-A Tennessee, and some thought he might make the MLB roster this year out of spring training. Instead, he has struggled offensively at Triple-A Iowa, hitting just .243/.333/.379, although the decent OBP indicates he's still drawing a fair number of walks.
Watkins is primarily an infielder, though he has played some games in the outfield, both last year and this year. For the moment, the Cubs still have just four outfielders on the 25-man roster (Nate Schierholtz, David DeJesus, Junior Lake and Cole Gillespie, and remember, Lake was primarily an infielder until this year). The Cubs really need to fix this soon.