I think they have enough players still to cover up for the injured player so not a big worry for Arteta if you ask me. Lot of players are very adaptable to other positions so Arteta has a very good set of options to choose from. But I feel it's better to develop other players as well by giving them chances. That way they can also help in matches in a better way and create a strong team.
As long as their opponent is not Manchester City but if their opponent is Manchester City it will not be easy even though there are several substitutes who can be an option.
Manchester City is still a frightening specter as an opponent so when they try to play without full strength then this becomes very difficult to be used as an advantage for Arsenal.
They are a good club but Manchester City are currently much better which makes it complicated for them.
By losing their core players it is the same as Arsenal not having full strength and that could be used as an opening for Manchester City in dominance in the match.