The 24-year-old, who has made 88 appearances for Villa, signed a new four-year contract in January but has found first-team chances in short supply since Tim Sherwood's arrival as manager in February.
The former England Under-21 has made just four appearances under Sherwood, featuring once this season, and has been allowed to join the Sky Bet Championship strugglers.
He was the second defensive reinforcement to arrive at Ashton Gate on deadline day, with Liam Moore joining on loan from Leicester until January 4.
Source : PA
Source: PA