'Worst performance of the season': Arteta frustrated by defeat at Fulham
Arteta's men have now won just one of their last five league games to fall two points behind leaders Liverpool, having played a game more.
But while the Spaniard could cling to positives despite defeat to Aston Villa and West Ham in recent weeks, the Arsenal boss made no defence for his players at Craven Cottage.
"We weren't good enough," said Arteta. "The other day we lost a game (against West Ham) we fully deserved to win and today we were nowhere near the level.
"This one you have to isolate because it's the worst performance of the season."
A lack of a clinical striker has been pinpointed as the major flaw among Arteta's squad that may prevent them from winning a first league title in 20 years.
But Arsenal also kept just one clean sheet in eight games in December.
Arteta rejected suggestions he needs to further reinforce his squad in the January transfer window.
However, he warned his players that any such repeat performances will scupper their quest to dethrone Manchester City as champions.
"If we play like we played in the other 19 games we will be up there," he added.
"If we play like today, we will be nowhere near. Today was a really difficult day to swallow."
Arsenal remain in fourth, but could even drop out of the Champions League places before they are in Premier League action again in three weeks' time.
Fulham had lost their previous three league games without even scoring a goal.
The return of Raul Jimenez from suspension, though, proved the catalyst for an impressive display and three points for Marco Silva's side.
Jimenez slotted home the equaliser after Bukayo Saka had fired Arsenal into an early lead.
Bobby De Cordova-Reid then grabbed the winner just before the hour mark after Arsenal failed to clear a corner.
"Really the best way to finish 2023, definitely. Our ambition was to finish on a high and react from the last two games," said Silva.
"I really believe we deserve it. Over the 95 minutes we deserved it more."
