It was reasonable to expect a position player heading out in order to make a spot for the newly-acquired center fielder Carlos Gomez. Evan Drellich told us who the odd man out is:
<blockquote class="twitter-tweet" lang="en"><p lang="en" dir="ltr">Singleton to be optioned to make room for Gomez. Less clarity on Fiers. Prob not activated til needed. Pitched Wed. <a href="http://t.co/13Qqzc4uJ7">http://t.co/13Qqzc4uJ7</a></p>— Evan Drellich (@EvanDrellich) <a href="https://twitter.com/EvanDrellich/status/627147431025725440">July 31, 2015</a></blockquote>
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This is not unexpected. There were only three listed outfielders on the Astros roster prior to the move, while Evan Gattis, Chris Carter, and Singleton fought over the first base and designated hitter spots. Singleton, who has options remaining and is the youngest of the three, was the logical choice.
Mike Fiers, the other player acquired in Thursday's big deal with the Brewers, will be added to the roster no later than Sunday. It's presumed a pitcher will be axed for him, of course, perhaps Vincent Velasquez, who's to-this-point fragile health is being protected in the bullpen currently.