Speaking to reporters, the 42-year-old said: "Playing with ten men always is an issue. The truth is, when you analyse it, three different actions and the outcome of them, the reasons are very different. Regardless of that, we cannot continue to play with ten men at this level.
"We need to eradicate that, it's clear. The reasons, how - it doesn't matter. We have to focus. We cannot continue to play with ten men, easier to say it than to get it done. 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."
When asked if Arsenal would appeal Saliba's red card, the manager added: "I leave that one to the club to understand the circumstances. The examples that are very clear in the same position and they will have to decide."