Elphick left Saturday’s 4-0 win over Derby on a stretcher and a scan has since revealed he tore a ligament at the base of his foot.
Though not as serious as first feared, the injury is expected to keep the 31-year-old sidelined until mid-April.
The timing is dreadful for both Elphick and Villa, who are aiming to mount a late play-off charge following the return to fitness of Jack Grealish.
With Alan Hutton also facing a lengthy spell on the sidelines with an ankle injury, boss Dean Smith suddenly finds himself with a paucity of options in a defence still missing both Axel Tuanzebe and captain James Chester.
The latter pair are not expected back until after this month’s international break at the earliest, meaning Villa must enter a potentially season-defining week with loan duo Kortney Hause and Tyrone Mings as their only recognised centre-backs.
Smith’s men face promotion rivals Blues, Nottingham Forest and Middlesbrough in the space of seven days, beginning with this Sunday’s Second City derby at St Andrew’s.
Elphick, meanwhile, has seen his hopes of earning a new deal at Villa Park suffer a setback.
The former Bournemouth skipper, one of several players out of contract in the summer, had started Villa’s last 10 Championship games after being recalled by Smith from Hull, where he spent the first half of the season on loan.