So far Gabriel Jesus has been a very important player in the Arsenal team and Arsenal's excellent game so far, of course, has a very large share of Gabriel Jesus and with the absence of Gabriel Jesus of course it will greatly affect Arsenal's performance.
however it all comes back to Arsenal coach Mikel Arteta how to handle this.
and so far due to the world cup we can see players who have improved performance and also injured players, it will all have an impact when they return to their respective clubs, be it positive or negative changes.
Jesus and Zinchenko was are City main team players who have become very important players in the Arteta team. For Guardeola, their absence is noticeable this season, did he really think that if so many important players left the team (remember Sterling went to Chelsea) his team's game would not change? But the season is not over yet, perhaps in the end it will turn out that he was right. )
The absence of Gabriel Jesus is a big blow to Arsenal and Arteta but they will not sit back and complain. They are lucky it happened when enough time will be given them to plan their next move. It is now left for Arteta to decide to get a striker by January or decide to use Nketiah who also is a good striker till when Jesus will recover from the injury. There is time for him to make decisions and i wouldn't want to see him make a free fall from the top.