Manchester United striker Zlatan Ibrahimovic and defender Marcos Rojo have both suffered cruciate knee-ligament injuries and face lengthy spells out of action.
Ibrahimovic landed awkwardly when challenging for the ball during the Europa League quarter-final second-leg win over Anderlecht.
The ex-Sweden international is United's top scorer this season, with 28 goals.
Rojo was replaced on 23 minutes after colliding with a visiting player.
Ibrahimovic, 35, joined the club on a free transfer from Paris St-Germain last summer but is yet to agree an extension to his one-year United deal.
Rojo's injury leaves United manager Jose Mourinho short of options at centre-back with England internationals Phil Jones and Chris Smalling already on the sidelines.
Eric Bailly and Daley Blind are United's only fit senior centre-backs heading into Sunday's game at Burnley (kick-off 14:15 BST), with the Manchester derby at Etihad Stadium to follow on Thursday.