Arsene Wenger has criticised Arsenal for falling to a "very frustrating" 2-1 loss at Bournemouth on Sunday.
Hector Bellerin had given the Gunners the lead on 52 minutes, but Callum Wilson and Jordon Ibe struck back midway through the second half to give the Cherries all three points.
Arsenal are now winless in five games in all competitions and five points adrift of fourth place in the Premier League table, prompting a disgruntled reaction from Wenger.
"We were 1-0 up and suddenly we lost two goals and we don't know where they came from," the Frenchman told BBC Sport. "It is very frustrating.
"Overall we have to look at it in a very objective and harsh way we made mistakes we should not have made.
"The team that fights against relegation will fight and you cannot afford any concentration mistakes."
Arsenal return to action on Saturday with a Premier League home clash against Crystal Palace.
