The Gunners could have secured their spot in the Premier League's top 4 for the first time since 2016 with a victory over Tottenham on Thursday, 12 May.
Instead, Arteta's side collapsed to a 3-0 defeat in the north London derby while also losing defender Rob Holding to a senseless red card just after the half-hour mark.
The Spanish boss has been criticized for not bringing on a central defender to replace Holding following his dismissal, as Spurs moved just one point behind Arsenal in the race for a Champions League spot.
Sinclair believes the team's lack of discipline comes from the manager, as he told talkSPORT:
“I struggle to understand how they've gone into that game, they've had six red cards this season, Gabriel, Xhaka, Martinelli, Holding, the list goes on. Look at the Man City game, every time they go into a big game, they have head loss. For me, it's not one individual player, it has to come from the manager, he's agitated, he's animated on the side."
"Even his comments after the game, he's almost trying to give his team excuses. Don't give the team excuses, they've got to be better, they have to be more controlled, they have to be more disciplined in big games like that. At the moment, they're not getting it, the reason they're not getting it is coming from the leader.”
Arteta rages at referee following Arsenal defeat
After a damaging loss at the Tottenham Hotspur Stadium, the 40-year-old could barely contain his anger towards referee Paul Tierney, who gave a penalty to Spurs as well as a red card to Holding.
Following the final whistle, Arteta was asked about Tierney's performance, to which he replied (as per Football.London):
"If I say what I think I am suspended for six months. I am allowed to give my interpretation of what I thought, but I do not like to lie. I cannot say what I think, I will be suspended."
"The referee has to make the decision and react in football. To take the risk in the situation didn't make any sense. I am so proud of my players, ask the referee to come here and explain his decisions. That's his decision, such a beautiful game was destroyed here."