A deflated Arsene Wenger was left to dwell on the double blow of Arsenal's surprise 2-1 home defeat to Watford and an injury setback for Aaron Ramsey.
The Frenchman, serving a touchline ban, watched on at Emirates Stadium as the Hornets raced into a 2-0 lead inside 13 minutes, with ex-Tottenham defender Younes Kaboul's free-kick deflecting in off Ramsey before Troy Deeney struck from close range.
Alex Iwobi reduced the deficit early in the second half and the Gunners dominated possession, but Lucas Perez's fierce strike against the crossbar five minutes from time was as close the hosts came to a leveller.
Commenting on Ramsey, Wenger said: "He has a calf strain. We don't know how long he'll be out for yet."
The 67-year-old was scathing of his side's performance, which came following a stunning display in Saturday's 5-0 FA Cup win at Southampton and resulted in a first home defeat in the top flight since the opening day - leaving their Premier League title hopes in tatters.
"It was obvious we lost duels and were not sharp enough," he said in quotes reported by BBC Sport.
"It looked more mentally that we were not ready for the challenges. We were unlucky for the first goal which was deflected after a soft free-kick.
"It took us a while to get into the game, it was all us in the second half and we were unlucky not to get something from it.
"You look at the facts and we were beaten in the duels. When you play at home in our position, that is not normal. Everybody in the Premier League is strong physically and 90 per cent is not enough.
"We knew the solution was going wide, but we were not patient enough and wanted to give too many long balls. We did not pass the ball quickly enough and we have to stick to our game, then we are always dangerous.
"Where does it leave the league? We lost and we want to respond in the next game. You can only have a chance if you win your games. I knew exactly what we were preparing for, but we have to learn from it."
With Chelsea having drawn against Liverpool, Arsenal slipped nine points off top spot ahead of Saturday's visit to the league leaders.