Casemiro could miss Manchester United's Europa League last 16 first leg on Thursday, according to reports.
United will face Real Betis at Old Trafford after beating Barcelona in the round of 32 last month.
They will be hoping to bounce back from their 7-0 humiliation at the hands of Liverpool in the Premier League on Sunday.
Casemiro has been a vital player for United this season since joining from Real Madrid in the summer.
But, according to ESPN, he picked up an injury in the game against Liverpool.
It is suggested that the 31-year-old will be assessed by medical staff ahead of the game with his injury status unclear.
He's played 35 times for the Red Devils so far this season following his £65million move from Spain.
The Brazilian helped Erik ten Hag's side to their first trophy under the Dutchman last weekend when they beat Newcastle to lift the Carabao Cup at Wembley.
He has proved to be instrumental in the side's upturn in form this year, with the possibility of winning the quadruple still on.
He struggled against Liverpool, however, and was one of several players that made regular mistakes as Jurgen Klopp's side tore through United.
Ten Hag's outfit will have their sights set on winning the Europa League towards the back end of the season, but must get past Betis, who are fifth in LaLiga, first.
The second leg of the tie will be played in Spain next week.