Arsenal boss Mikel Arteta fumed after Brighton's 2-1 victory over his side at the Amex on Saturday afternoon.
Two late goals from the Seagulls sealed victory for the home side after Pepe's excellet 68th minute strike put the Gunners ahead.
Lewis Dunk levelled seven minutes after the former Lille man's superb left-footed curler appeared to set Arsenal on course for three points on the south coast.
Neal Maupay then powered home a late, late winner to clinch the first win of 2020 for Graham Potter's side.
Speaking after the match a visibly furious Arteta told BT Sport: "Defeat was very difficult to take. It was unnaceptable.
"We missed so many chances. We didn't compete for the second goal. At this level you cannot give goals away. We cannot accept that."
Defeat sees Arsenal remain in ninth place with the prospect of European football fast receding.
To cap a miserable week for the north Londoners, keeper Bernd Leno was stretchered off in the first half following a late challenge by matchwinner Maupay, with fears growing over the German suffering a long-term injury to his knee.
Arteta refused to blame Maupay, saying: "No player sets out to injure another [but Leno's injury] didn't look good."