Mikel Arteta said that the team needed to apologize after a poor performance resulted in a third-round FA Cup defeat.
The difference at the City Ground was Lewis Grabban's late strike, as Forest shocked the Gunners again, having beaten them 4-2 at the same stage in the previous year.
Arteta made several changes to his team, but still included some of them in the starting XI.
Arteta told ITV that they were not good enough.
Forest upset the team again.
The draw for the fourth round of the FA Cup.
I don't want to use excuses, I expect the team I put out to do better and when you don't in the cup you are out.
We didn't put in the level to win the game against Forest and that showed we weren't capable of winning away from home. We have not done it today. Today's work is not close to the level and standards that are required.
Arteta said that they needed more drive, more hunger to win at any cost in every single action. We weren't at our level.
First of all, I'm really disappointed with the performance. Not with the attitude but how much purpose we have and how determined we were to change the game when it was difficult to play against.
Lewis Grabban won the FA Cup.
I have played games like that for 18 years and I know how difficult it is to come here. We have to face it in a different way when we do that.
It is really hurting. To get out of a competition that is related to our history is very difficult.
Even though they had more possession, they didn't have a single shot on target.
After just 34 minutes of the match, Nuno was hooked and he threw his gloves to the ground.
Arteta said that he did it to improve the performance of the team.
Nuno Tavares was taken off after 34 minutes.
I have to make a decision to improve the performance of the team when it's not going in any other direction.
The next three games will be a chance for the team to improve.
They face either Spurs or Liverpool in the Carabao Cup semi-finals on January 13 and 20 and either side of a trip to north London rivals.
Steve Cooper said he was proud of his players.
He said that they had a clear game plan against the good team. We wanted to be brave with our pressing and get at them on the counter.
I'm very proud of the boys. I hope the players now believe in what we're doing because it's brilliant to get through.
Grabban is the club captain. He's experienced and we work together to use him. He scored after we brought him on.