Player who injured is definitely will affect the result since the substitute player isn't as good as the main line up, I only talk about the skill while chemistry, strategy etc also give a big effect to other players. Not many teams have a balance main line up and substitute player, I think only Brighton have this, whoever who play, the result will not be different.
Let's see how Brighton faces Manchester City this week at the Etihad Stadium, because currently Manchester City's appearance is starting to look different even though it is still strong enough to win. But if Brighton can beat Manchester City at the Etihad Stadium, this will actually be extraordinary for Brighton because it will continue to create increasingly exciting competition in the Premier League standings table. However, I am also still not sure about Brighton in terms of beating Manchester City at the Etihad Stadium.
But, if we consider the odds available, at least Manchester City remain the favorite team to win. Perhaps, Manchester City are projected to win on paper, because the odds gap is also fairly wide. But unfortunately, if we consider about performance then yes, at least Brighton will also still have a good chance to provide difficult resistance to Manchester City in this match. Because after all, Manchester City and Brighton currently also only have a two-point gap in the Premier League standings. Therefore, although this match will be played at Etihad Stadium, I guess it is likely that Manchester City will still not be easy to win in this home match.