At the beginning of the summer, defence was Guardiola's priority, as demonstrated by the signings of Kyle Walker, Danilo and Bejamin Mendy. With Vincent Kompany's constant injury problems and the inexperienced nature of John Stones, Guardiola wants to bring in an experienced head to play alongside him.
Whilst Nicolas Otamendi is seen as a capable back-up, if he succumbs to injury then Eliaquim Mangala is not seen as a suitable stand-in.
Virgil van Dijk and Leonardo Bonnuci were early targets for City but for various reasons neither ended up signing. The homegrown rules are also something which need addressing at City and so the centre-back which City are looking for ideally has to be home-grown, dependable and inexpensive, especially given how much they have already spent on defensive reinforcements this window.
Therefore, Jonny Evans is a suitable candidate as he ticks all three boxes. However, Evans' current manager Tony Pulis is unlikely to give him up without a fight.
The 29-year-old was recently made captain at West Brom following Darren Fletcher's departure and Pulis sees him as one of his most important players.
The Baggies are still looking to strengthen defensively and so it is unlikely they will let their skipper go without an incredibly appealing bid.
Should a deal be agreed between the two clubs, Evans would also have to deal with the backlash from fans of his former club Manchester United if he does decide to join their rivals. City's pursuit of Evans, whilst it does make sense, will not be an easy one to get over the line.