The 29-year-old centre-back, who signed a two-year deal at Bramall Lane in the summer after a loan spell from Watford last season, is yet to agree personal terms.
Dewsbury-born Bromby started his career in West Yorkshire at Liversedge before going on to play for Sheffield Wednesday, Watford, Mansfield and Norwich, as well as the Blades.
He signed a two-year deal at Bramall Lane in the summer, but has yet to play a league game for them this season.