the 4th position is not fixed yet which club is worth it to fill that zone, but I am sure The City will lock it to guarantee that they are defending champions from the last session. we certainly have doubts because they are not in the best performance, but based on what they did in the last match, The City won't let another club like Chelsea, or Newcastle occupy the position. Arsenal and Nottingham have not yet fixed if they will remain in that position because there are still many matches left which will probably will be replaced by other clubs if their performance decreases based on how much player injured they got.
Fourth position in league is still available and many clubs want to take it. And I also think Manchester City is most likely team to get it even though they have not been playing well all time this season. Fact is that they won their last match shows that they really want to keep their title from last year. Chelsea and Newcastle also have chance but Manchester City has more experience and stronger team which gives them an advantage. Arsenal and Nottingham are also trying to get the fourth spot but it is not safe for them yet. There are still many games left to play and if they do not keep playing well other teams might catch up and take their place. If some of their best players get hurt that could also hurt their chances and make it hard for them to stay where they are.