Antonio Rudiger has reportedly verbally agreed to a deal with Real Madrid which means the German center-back is on his way out of the club as a free agent.
Rudiger's performances in the last 18 months since Thomas Tuchel took over have been nothing short of world-class which is what made the thought of losing him for free so unbearable to all associated with the club.
And now that the worst appears to have happened, the club must now chart a way forward and look for an adequate replacement which is where the hard work is.
Elite centre-backs are at a premium in European football right now, there simply aren't that many of them around and the list becomes even shorter when availability is factored in.
On top of that, to adequately replace Rudiger while maintaining the same shape and system, Chelsea needs a left centre-back, which is an elite central defender who is at his best on the left of a three-man defence.
When all these search filters are added, only one viable option pops up and that is Italian central defender Alessandro Bastoni who is Chelsea's best bet to replace the departing Rudiger.
Bastoni and Rudiger have numerous similarities beyond their shared left centre-back position, all of which should make the signing a no-brainer for Thomas Tuchel.
Bastoni is the same height as Rudiger with both players standing at six feet two inches tall which means Chelsea will not be missing the German's imposing physical frame if they replace him adequately.
Much like Rudiger, Bastoni is confident and comfortable on the ball, often making long strides out of the Inter Milan defence just as Rudiger is known for at Chelsea.
As a left-footed player on the left side of the defence, Bastoni often shows off his long-range passing ability without having to adjust his body as the right-footed Rudiger would.
Bastoni is not better than Rudiger yet but there are some upsides to his game that suggests that he will be the better of the two players someday and a worthy investment for Chelsea going forward.
The 23-year-old Italian grew up playing in this position, three-man defences are the norm at every level in Italy and Bastoni was born to play that role, unlike Rudiger who had to be conditioned into it by Tuchel.
Bastoni is also more versatile because he can play as a left-back and has featured in midfield for Inter Milan recently where he also held his own.
The first option is to keep Rudiger at the club and understandably so but in the event that proves impossible, signing Bastoni is the next best solution for Chelsea if they want to maintain this current defensive structure.
There is simply no like-for-like Rudiger replacement that is better than Bastoni, except Tuchel opts to replace Rudiger indirectly by switching up the system entirely.