West Bromwich - Arsene Wenger described Arsenal's 2-1 defeat at West Bromwich Albion as the "perfect nightmare" after midfielders Francis Coquelin and Mikel Arteta added to his injury problems.
Arteta's own goal, coupled with a late penalty miss by Santi Cazorla, ended the Gunners' six-match unbeaten Premier League run and dented their title challenge.
And Gunners boss Wenger, already without Alex Oxlade-Chamberlain, Theo Walcott, Aaron Ramsey and Danny Welbeck, suffered further setbacks as he lost Coquelin to a knee problem and Arteta to a recurrence of a calf injury.
Both players will be assessed and are doubts for Tuesday's Champions League home match against Dinamo Zagreb, which Arsenal must win to stand any chance of staying in the competition.
"It was a very bad afternoon for us. We had 70 per cent possession, we scored an own goal, we missed a penalty, we gave away a goal from a set piece. That's perfect to make the afternoon a nightmare," Wenger said.
"We missed open goal chances too. I believe that West Brom fought with 100 per cent commitment as well. You have to give them credit for that.
"We landed a huge blow when we scored. We just had to make sure that they didn't come back with an easy goal.
"We lost a bit of focus at 1-0. After 35 minutes, we were 1-0 up. After 45 minutes, we were 2-1 down. Our defending on that level was very, very poor.
"On top of that, we have two more injuries. One is a recurrence of a calf problem for Arteta, one is a knee problem for Coquelin. I don't know how severe that is. We'll know tomorrow (Sunday)."
Wenger refused to blame Cazorla for his missed penalty, which came amid confusion, as it initially appeared as though referee Mark Clattenburg had ordered a retake for encroachment.
As it turned out, Clattenburg had penalised the midfielder for taking two touches as he slipped; with the rules not allowing a penalty taker to touch the ball again until another player has done so.
Arsenal were consigned to defeat despite an early goal from Olivier Giroud who, like France team-mate Laurent Koscielny, played eight days after being caught up in the horrific Paris attacks.
Giroud and Koscielny were playing for France in a friendly against Germany at the Stade de France, which was targeted by three attackers who blew themselves up outside the stadium, with the explosions heard during the match.
Wenger said that he had no doubts about fielding either player, citing their professionalism.
"They were highly focused and had a desire to play," Wenger said.
"We produced enough to win the game. I don't know about the influence of what happened (in Paris) on the game.
"For my part, I would not explain our defeat by that. I think it's sad. We are all down. But when you're on the pitch, you're on the pitch."
West Brom manager Tony Pulis, whose side drew level through James Morrison before Arteta's own goal, acknowledged that his players had gained victory despite not being at their best.
"There have been games here this year where we've been disappointed that we've lost," he said.
"Today, I thought Arsenal were very good - especially in the second half, when they ramped it up. (Alexis) Sanchez was wonderful in his movement and his play.
"You've got (Mesut) Ozil, Cazorla, players of that quality too. They're wonderful talents.
"It's a great result. The lads are very pleased. They deserve it for the effort they've put in.
"But we've played better and done better and not got the results."