Kevin De Bruyne is one of the most valuable players for Manchester City without doubt. His absence due to injury is really unlucky for them as well. However I don't think this would affect them deeply anyway. Because they are still one of the strongest teams in Europe now. They are full of world stars playing in coherence together.
There has been some drop in their form recently but it is no problem at all. I remember Manchester City having way worse times in one season and they were way behind the leader. But they still made an unforgettable comeback and won the title by a serious point gap.
For sure Kevin d bruyne injury is very unfortunate because of his great impact in the midfield but Man city is one of the teams in the world with experience, great and tactical players so even without Kevin d bruyne they can deliver their best on the pitch but brighton and hove albion has also been a competitive side since last season, so I see some drama in this game but whichever be the case, let the best team win