The £25million January signing of Wilfried Bony has left City with one more non-homegrown player in their squad than they are permitted to field in European competitions this season.
As punishment for breaching UEFA's Financial Fair Play restrictions, City are restricted to naming just 16 foreign players in their squad, rather than the usual 17.
Pellegrini has, as yet, given no public indication which player he intends to omit but his revised squad for the second half of the season must be submitted to European governing body UEFA by 11pm Tuesday.
Speculation has suggested the players most likely to be at risk are back-up goalkeeper Willy Caballero, full-backs Aleksandar Kolarov and Bacary Sagna, and striker Stevan Jovetic.
In the first part of the season the decision was more straightforward as City opted not to register injured striker Alvaro Negredo, who subsequently joined Valencia on loan.
But now, as they prepare to face Spanish giants Barcelona in the last 16, a player who featured in the group stages must miss out as it seems inconceivable the club would not register Bony.
De-registering Caballero might be the most straightforward option given that he does not seem likely to supplant Joe Hart as number one, but it arguably carries the greatest risk.
Should Caballero not be included, an injury or suspension to Hart would leave Pellegrini needing to turn to third-choice Richard Wright, the veteran who has not played since joining the club in 2012.
Jovetic could be vulnerable given his limited involvement during 19 injury-plagued months at City while Kolarov has become second choice to Gael Clichy at left-back since a spell out injured in November.
Right-back Sagna has also been behind Pablo Zabaleta in the pecking order since joining the club from Arsenal last summer but his versatility could count in his favour.
The only other realistic alternatives to be left out could be midfielders Fernando or Fernandinho, but with Yaya Toure suspended for the first leg of the Barcleona tie later this month, they would seem unlikely candidates.
Frenchman Clichy does not feature on the foreign quota as he qualifies as homegrown, as does Belgian centre-back Dedryck Boyata.
Source : PA
Source: PA