Arsene Wenger has ruled out Aaron Ramsey until the new year, while Olivier Giroud faces a lengthy spell on the sidelines.
Arsenal take on Crystal Palace at Selhurst Park on Thursday, needing three points to keep pace with Liverpool and Tottenham in the race for a top four finish.
Wenger revealed he is contending with a trio of absentees for the big game, but offered a glimmer of hope over Giroud's rehabilitation.
“Monreal, Giroud And Ramsey are out. Nacho ten days, Giroud four to six weeks but he is a quick healer, Ramsey beginning of January," Wenger said.
“Giroud will be back at the beginning of January. He suffered the injury in the middle of December so four to six weeks is January 10-15."
Arsenalsquad : Cech, Ospina, Mertesacker, Holding, Mustafi, Koscielny, Chambers, Debuchy, Bellerin, Nelson, Kolasinac, Maitland-Niles, Coquelin, Wilshere, Xhaka, Elneny, Ozil, Iwobi, Sanchez, Welbeck, Walcott, Lacazette.
Crystal Palace, meanwhile, have Christian Benteke available again.
The striker served a one-match ban as Palace drew at Swansea on Saturday and he is expected to be restored to the starting line-up by boss Roy Hodgson.
Jason Puncheon remains available for selection despite being charged with possession of an offensive weapon and assault while Joel Ward is still struggling with a groin problem.
Crystal Palace squad: Speroni, Hennessey, Kelly, Dann, Tomkins, Riedewald, Schlupp, Van Aanholt, Souare, Townsend, Loftus-Cheek, Puncheon, Cabaye, Milivojevic, McArthur, Mutch, Ladapo, Sako, Kaikai, Zaha, Benteke.