The injury also means that the 30-year-old - who is on loan from Premier League team Manchester City - risks missing this summer's World Cup in the United States, Canada and Mexico.
"We think he will probably need surgery, but it is still not fully confirmed. However, it will probably mean he is out for the rest of the season," said manager David Moyes.
Grealish's last international match for England was against Finland in October 2024. However, his play at Everton has put him in the World Cup conversation.
