Arsenal head coach Mikel Arteta has said his team need to "eradicate" the ill discipline that has seen them pick up three red cards in eight Premier League games this season.
William Saliba's red card in the 2-0 defeat at Bournemouth followed those of Declan Rice and Leandro Trossard earlier this term.
"Playing with 10 men always is an issue," Arteta said at his news conference ahead of Arsenal's UEFA Champions League game against Shakhtar Donetsk on Tuesday. "The trust is, when you analyse it, three different very actions and the outcome of them, the reasons are very different.
"Regardless of that we cannot continue to play with 10 men at this level. We need to eradicate that, it's clear. The reasons, how; it doesn't matter. We have to focus."
The loss to Bournemouth was Arsenal's first of the campaign. In the previous games where Rice and Trossard were shown red cards, against Brighton and Manchester City, the north London side managed to earn a point.
Arteta added that his team needed to use the "pain" of their defeat as motivation for their upcoming games.
"We cannot continue to play with ten men, easier to say it then to get it done," he said. "Specific moments. Reacting, we have a defeat. Very specific conditions as well.
"Let's move on, take that pain we have and use it tomorrow night."
Club captain Martin Ødegaard and star winger Bukayo Saka both missed Arsenal's trip to Bournemouth with injuries.
Arteta said Saka could return in time for Tuesday night's game at the Emirates, though it comes too soon for the Norway international.
"They are closer. Both progressing well," he said. "Martin not fit. With Bukayo let's see how he is with the training session later on."