In response to charliedarling's comment:
If I am the Red Sox I buy Sweeney a first baseman's glove and start hitting him balls as soon as he sets foot in Fort Myers.
In fact and better still, if I am Ryan Sweeney (and don't already have such a glove) I go out and buy one TODAY, right this second even, and start making it comfortable on his hand. It could be what keeps him in the major leagues for another season or two.
He HAS to be athletic enough to learn to play first base in the next two months if he can play center field on the major league level even if he has never played an inning at first base yet.
Why would you move a pretty good defensive CFer to 1b? If I was Nava I would do my best to convince the team I could play 1b or find a nice apartment in Rhode Island.