Manchester United look to Arsenal to do them a favour
City were beaten by Real Madrid in the Champions League semi-final on Wednesday and they now face Arsenal on Sunday knowing they still have to qualify for next season's competition.
Pellegrini said: "If you are not in the top four it's a disastrous season but if you win the Champions League, FA Cup and League Cup, it's a very good one."
Some of the Premier League's most frequent Champions League qualifiers from the past decade could yet fail to make it into the 2016-17 edition.
Ninth-placed Chelsea, winners in 2012, know they will not finish in the top four.
Liverpool have the slimmest of possibilities to make the top four but could yet qualify for the Champions League as Europa League winners, having made the final in Basel, where they will play Sevilla on 18 May.
One win from the final two games of a season that ends at home to relegated Aston Villa on 15 May will be enough for Arsenal.
It leaves City battling with fifth-placed Manchester United and sixth-placed West Ham, who play each other in the final game at Upton Park on 11 May. But with United beating Norwich on Saturday whilst the Hammers were turned over by Swansea the picture looks even tougher for City - Manchester that is.
The Blues are just a point ahaed of their Manchester rivals who have West Ham and Bournemouth left to play.
For once United fans will want arch rivals Arsenal to do them a favour because realistically United are looking to overhaul City not Arsenal.