Arsene Wenger described Arsenal's defeat at Stoke as "a massive setback" to their Premier League title chances.
"It is not slightly worrying, it's a big worry to lose a game like that," said Arsenal manager Wenger.
"In a game like that, we didn't produce the performance that we wanted."
He added: "To win a title when you are expected to perform, you have to perform, it's as simple as that. It was a massive setback."
Arsenal face a crucial month as they attempt to win their first Premier League title since 2004.
After FA Cup and Champions League games against Everton and Bayern Munich respectively, they take on three of the top five teams in the Premier League - Tottenham, Chelsea and Manchester City - in a two-week period.
Wenger dismissed suggestions that his team looked fragile, but said they lacked an attacking thrust at an important stage of the season.
The Frenchman also felt the penalty awarded by referee Mike Jones was "a gift" for Stoke after the ball struck Laurent Koscielny's hand as Walters tried to lift it over him.
"It was a good defensive performance and overall we are unlucky to lose this game," said Wenger. "Offensively we didn't create enough and it was poor, considering our standards.
"At the end of day we didn't score because of that. We conceded the goal, that was a nice gift from the referee, but it can happen.
"[Koscielny] is one yard away, he has not got the time to take his hand away from the ball. He has no intention at all, but of course we can't influence the decision of the referee."
Arsenal have had a miserable run of results at the Britannia Stadium, with only one win from their last six visits in the league.
Despite several heavy challenges on his striker Olivier Giroud, Wenger chose not to talk about Stoke's robust approach.
He said: "You have to give credit to Stoke, they defended well with resilience and they made the game very physical. We knew before the game, they have the highest number of fouls in the Premier League but we didn't cope well enough with it.
"Honestly I don't want to talk about the referee. I have nothing to say about [fouls on Giroud], I'm long enough in the game to make my own judgement and I prefer to concentrate on our performance."