Major league rosters expand September 1st. This means the Twins can activate anyone on the 40 player roster on September 1st. In the past the Twins have usually waited until the minor league seasons are finished to call up players they just want to take a look at but they will add players immediately if they think can help in the pennant race. So who are the likely call-ups:
Catcher - Morales is the most likely guy here. My bet is they call him up September 1 so that they can DH Mauer without worrying about losing the DH. They might give Butera a callup later given his defensive skills.
Infield - I think Tolbert and Buscher are probably givens. Buscher may even be added August 31st to put him on the playoff roster. Plouffe and Tolleson are both on the roster, but its not clear either one can help in a pennant race. My guess is these guys get call-ups only if the Twins are all but finished when the Rochester season ends.
Outfield - The Twins have a surplus in the outfield already. But they may take one more look at Jason Pridie. Pridie would provide a pinch runner and more flexilbility in how Young and Gomez are used.
Pitching - I think the Twins will add enough pitching so that the bullpen is overstocked. Dickey, Swarzak, Mulvey are already on the 40 player roster and likely to be added for the September run. Given the pitching struggles, any of those three could find themselves on the playoff roster if they get hot in September.
There are a lot of players who are not on the roster that might warrant a look. But there does not appear to be any players on the 40 player roster that the Twins are likely to release in order to provide room for them. Pridie or Dickey would be possibilities if they are ready to give up on them. Deibinson Romero is a young A-ball player who might pass through waivers. Luke Hughes would be the other player they might be ready to give up on. I think all of those are doubtful The most likely scenario is that they wait until the season is over and guys like Crede, Redmond and Cabrera leave as free agents to start promoting players. That means this year September call-ups are going to be limited to the players already on the major league roster.