Per Mike Berardino, Eddie Rosario has been optioned to AAA. He was benched in Wednesday's game against the Tigers after stealing 3rd despite being down 4 runs.
Rosario has been struggling mightily this year, batting just .205/.224/.320, and showing very little signs of improvement. His main problem is a lack of discipline at the plate, and it was an issue last year as well (15 BB, 118 SO). The difference this year is the hits aren't coming, so his batting average can't hold up his stats. He also had an unsustainable number of triples last year (15), inflating his SLG%.
Right now the favorite to replace him seems to be newly signed Robbie Grossman (not Rex), although other options could include Max Kepler and Byron Buxton.