The irony is, it's because of bullpen problems that he was brought up. So, here's the situation. Alex Presley was optioned to AAA to make room for Andrew Lambo and try him out in right field (he's having a big year between AA and AAA). But, due to the bullpen being seriously overworked in the last week or so, they had to option Lambo to add a pitcher (Kris Johnson, and then Ryan Reid). As you know, when you option someone, they must stay at AAA for at least ten days before they can be brought back. Neither Presley nor Lambo were down for ten days.
Both Starling Marte and Jose Tabata are injured, but neither serious enough to go on the DL, which would allow either Presley or Lambo to be recalled. So, the situation is that they are short in the outfield and in the bullpen. Thanks to decent starts from Liriano and Burnett over the last two days, as well as Kris Johnson working six iinnings in relief on Sunday against Arizona, the bullpen is somewhat back to normal, but they were still short an outfielder, specifically someone who could play center in an emergency. So...enter Felix Pie.