Arsenal manager Arsene Wenger admitted his side face an uphill battle to finish in the Premier League top four after Saturday's dispiriting 3-1 defeat at West Bromwich Albion.
Craig Dawson scored twice as West Brom condemned Arsenal to a fourth defeat in five league games, which left them five points off the Champions League places.
Arsenal also lost goalkeeper Petr Cech to a muscular problem and Wenger revealed talisman Alexis Sanchez had sustained a potentially serious ankle injury.
"It's very worrying because we are not used to that. We have a hell of a task now to fight back," Wenger told Sky Sports at The Hawthorns.
"We need to improve and focus on the games coming up. There are many big games. We have to go away and recover and prepare well for the end of the season."
Cech hobbled off shortly before half-time, with David Ospina taking his place, while Sanchez, who cancelled out Dawson's opener, gave way for Alex Iwobi late on.
"We lost Petr Cech in the first half on a calf problem and after we lost Sanchez," Wenger said.
"He stayed on, but in the second half he was not himself so I decided to take him off. His ankle doesn't look good. When it doesn't go well, it's always the same."
Rival groups of Arsenal fans paid for planes trailing banners that were both critical and supportive of Wenger to fly over the stadium during the game.
A banner that read "NO CONTRACT #WENGER OUT" was seen flying above the stadium shortly before kick-off.
But in the 16th minute, with the score 1-1, another plane was spotted overhead with a banner that read: "IN ARSENE WE TRUST #RESPECTAW".
Wenger, Arsenal's manager since 1996, has come under pressure from fans after Arsenal were humiliated 10-2 on aggregate by Bayern Munich in the Champions League and dropped out of the Premier League top four.
The 67-year-old Frenchman is believed to have been offered a new two-year contract by the club.
Arsenal's support is split over Wenger, who won seven trophies in his first nine seasons as manager but has won only two FA Cups in the 12 years since.
Former Arsenal striker Thierry Henry delivered a damning verdict on the team's performance.
"They were nowhere near the desire and the commitment needed to win a game in the Premier League," he said.
Arsenal midfielder Alex Oxlade-Chamberlain apologised to the club's fans after the game, describing their performance as "not acceptable".