There is still plenty of time to make changes to their performance and I am also confident that Manchester City can get out of their slump and do everything to stay in the Champion League competition.
Manchester City still have 2 more matches and against PSG is their toughest opponent and if you look at the overall strength despite the slump that has hit Manchester City at this time I am still optimistic that Manchester City can win the match to advance to the play-off round.
They have at least 3 week to improve their performance till January 22 I think and that should be aprox.. the weeks. Till then, their Premier league games will tell if they already step up their performance or they are still declining but it seem to have changed a little in theirlast two games even though they still draw and lose one.
They have up to 5 to 6 games ahead of them before UCL plus FA cup

that should tell a lot .. besides, PSG is not also playing well in UCL.
Hence, I won't come to conclusion until after 3 games ahead in PL and like I said, it should tell a lot about their stand even though UCL is another phase on it's own.