Chelsea boss Thomas Tuchel admits Hakim Ziyech could be facing an extended spell on the sidelines.
The Moroccan winger looked in fine form during the first half of their UEFA Super Cup win over Villarreal.
He scored the opener for Chelsea, before a nasty collision saw him injury his shoulder and require substitution.
After the game, which Chelsea won on penalties following a 1-1 draw, Tuchel spoke about Ziyech's condition.
Tuchel said: "If you take a player out during the first half, it is serious.
"It was unfortunate because he has been a very decisive player in the last games."