Arsenal defender Rob Holding is expected to be out for about three weeks after suffering an injury in the warm-up against Manchester City last weekend.
Holding, 25, is expected to miss six league and cup games, starting with Thursday's Europa League group game with Rapid Vienna in Austria.
Dani Ceballos is nursing an ankle injury and will not play on Thursday.
Arsenal say the Spanish midfielder is being assessed before Sunday's Premier League home game with Leicester (19:15 GMT)
Former Chelsea midfielder Willian will also miss his side's opening Europa League group game with a calf issue.