Arsene Wenger admits Arsenal are in the midst of a "difficult moment" in the build-up to their crucial Champions League clash with Dinamo Zagreb.
The Gunners slipped to a 2-1 defeat at West Brom in the Premier League on Saturday after Santi Cazorla's penalty miss.
The midfielder lost his footing to balloon a late spot-kick over as Arsenal missed the chance to go top of the Premier League or even claim a point at The Hawthorns.
Boss Wenger claimed the defeat was a "nightmare" and, ahead of Tuesday's visit of Zagreb with Arsenal six points behind the top two in Group F, he knows they must recover.
"It is severe disappointment, we want to bounce back," Wenger said.
"Now we cannot change it and the only thing we can do is bounce back on Tuesday night. It is a difficult moment for us, yes.
"In the last two games, we took one point out of six and that is very difficult and very disappointing when you are on such a great run. We have to come back quickly and focus."
Mikel Arteta scored an own goal which proved to be the winner for Albion after James Morrison cancelled out Olivier Giroud's opener.
Arsenal's injury woes also grew after Francis Coquelin and Arteta joined a lengthy list who are already in the treatment room. Aaron Ramsey, Theo Walcott, Alex Oxlade-Chamberlain, Danny Welbeck, Tomas Rosicky and Jack Wilshere are among those sidelined.
"It looks difficult to have players come back Tuesday night," said Wenger. "I can rotate a bit within the squad but Ramsey will be short and Chamberlain will be short and they are the two closest.
"Honestly I don't know [about Coquelin]. I have to wait, maybe Monday, to see how big the damage is, at the moment he is on crutches."