It is still a rumor, we don't know how serious Chelsea to sign Maguire. I even think Chelsea current defenders are better than Maguire. Even if they are not strong enough but they don't score own goals at least. 
Harry Maguire is 30 years old, his market value is €20m. No team will spend €40m for Maguire, it is just nonsense to buy a player who has bad performance and he is no longer young defender. Moreover, €40m is overpriced since he is only valued €20m. I assume any club who is interested to sign him for below €10m.
Chelsea was completely unexpected where they were rumored to be buying Maguire from Manchester United. Even though there are still many other defenders that they can prioritize in this transfer window rather than chasing Maguire. I don't want to see the humor Chelsea makes in this transfer window because they sold a lot of quality players and bought players who didn't perform very well last season.Harry Maguire is 30 years old, his market value is €20m. No team will spend €40m for Maguire, it is just nonsense to buy a player who has bad performance and he is no longer young defender. Moreover, €40m is overpriced since he is only valued €20m. I assume any club who is interested to sign him for below €10m.
Chelsea need to bounce back next season and Pochettino needs to be able to bring in younger players to their squad instead of chasing Maguire. Indeed Chelsea have often made signings to their detriment such as Lukaku signing which now he is not included in Pochettino big plans for next season.
A Maguire transfer from Manchester United to Chelsea would be a surprise for several reasons. Maguire had a hard time in Manchester and I think besides the financial aspects he could also be a winner if Chelsea performs well and he can play a part in that success. But if Chelsea fails again, I can already read all the public allegations against the club and those responsible for the transfers because why would they sign players that underperformed when they themselves underperformed and are now trying to recover? Negative times negative is positive? Maguire is a high risk transfer if this really happens as Chelsea doesn't have the time to run some experiments with players who failed elsewhere.