Manchester United defender Lisandro Martinez could sit out the rest of the season after the Premier League club said the Argentina international suffered an anterior cruciate knee ligament injury in Sunday's 2-0 home loss to Crystal Palace.
Martinez was carried off on a stretcher in the second half with what looked like a serious knee injury after a challenge on Palace forward Ismaila Sarr.
"Assessment of the injury is ongoing to determine the appropriate course of treatment and the time scale for his rehabilitation," the club said on Thursday.
Martinez is also likely to miss World Cup qualifiers against Uruguay and Brazil next month.
Argentina top the South American standings with 25 points after 12 games, five points ahead of second-placed Uruguay.
Martinez joins a United injury list that also includes midfielder Mason Mount and defenders Luke Shaw and Jonny Evans, leaving manager Ruben Amorim with few options in defence.
Martinez had been an integral part of the defence, slotting in at left-sided centre back in a back three or in a back four.
The 27-year-old has made 24 appearances in all competitions this season and scored two goals last month – the opener in a 2-2 draw at Liverpool and the winner at Fulham in a 1-0 victory.
Martinez injured his medial collateral ligament last year, which had kept him sidelined for two months.
United are 13th in the Premier League and next host Leicester City in the FA Cup fourth round on Friday.