Arsenal midfielder Santi Cazorla could be out until March, manager Arsene Wenger has revealed.
The 30-year-old Spain international suffered a knee injury in the Gunners' 1-1 draw at Norwich last Sunday.
The club are already without midfield colleague Francis Coquelin for about three months following a knee ligament injury.
However, defender Laurent Koscielny and forward Theo Walcott could return to face Sunderland on Saturday.
Alexis Sanchez is out with a hamstring injury he suffered at Norwich, with Wenger defending his decision to play the Chile international against Norwich last weekend.
Sanchez had suffered a minor hamstring problem against Dinamo Zagreb in their previous game but had said he was fit to play.
Wenger told Arsenal's pre-match press conference on Friday: "Sanchez had four weeks' holiday [after the Copa America]. He was tested in some games, had all the sports science to play.
"No-one suggested he could injure a hamstring or back when he was pushed into a camera [pit]. That shocked everyone.
"I am not expert enough, but if you want to blame me, no problems."