The City defenders have been bit-part players in Pep Guardiola's starting XI at times this campaign as their title challenge faltered.
The former Premier League champions are interested in bringing in a centre-back, and scouts have kept an eye on the 29-year-old Senegal ace.
It is understood Napoli have already been in contact with City over the availability of both Otamendi and Zinchenko.
And that could pave the way for them to be used as part of a £65million-plus swoop for Koulibaly, regarded as one of the best defenders in Europe.
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