Bristol City midfielder Andreas Weimann will need knee surgery to repair anterior cruciate ligament damage.
Weimann, 29, was injured during the Robins' 1-1 draw against Swansea City on Saturday and could now be out of action for up to nine months.
On loan full-back Steven Sessegnon, 20, also picked up a hamstring injury in the same fixture.
He has returned to parent club Fulham for further treatment with no immediate timescale put on his recovery.
Austria international Weimann has made more than 100 appearances since joining Bristol City from Derby County in July 2018.
Sessegnon's only Championship start since arriving on a season-long loan in September came in the home draw with Swansea.
Bristol City could move back up to second in the Championship if they can avoid defeat against Bournemouth on Wednesday evening.