Marcos Alonso arrived at Stamford Bridge in 2016 following a £24m move from Fiorentina. To many Chelsea supporters, this was a questionable signing by new manager Antonio Conte.
Despite having a relatively successful spell under Conte, Maurizio Sarri's new system has exposed his many defensive flaws, with Alonso losing what looked like a guaranteed starting spot in the Blues' squad.
When used in Conte's 3-4-3 system, Alonso was always deployed as a left wing-back. This allowed the Spaniard to get forward and make a real connection with Eden Hazard on the left flank. Alonso could put his defensive responsibilities in the back of his mind because he always knew there would be a center-back covering for him.
When Sarri took over at the helm this season he switched the formation to his preferred 4-3-3. By slotting in Alonso on the left of a back four, he expected him to do much more defending while staying at the back. This turned out to be a major flaw in his game, despite some early-season success.
Over the course of the last few months, Alonso's relationship with his teammates on the pitch has dwindled immensely. He no longer produces the same fluidity with Hazard on the left flank and you can see the frustration on his face, game in and game out. There have been many instances in which he has made angry gestures to other defenders on the pitch for mistakes which were ultimately his own.
Alonso had a particularly bad game when the Blues were crushed at the hands of Manchester City on Sunday night. Although the defence as a whole was quite poor, Alonso's night can be summed up by City's first goal. The Spanish defender left Bernardo Silva wide open on the left, giving the opposing attacker too much space to put in a perfect cross. Raheem Sterling ended up with the goal on the far post, but it is impossible to overlook the positioning mishap by Alonso.
With Chelsea constantly overexposed on Alonso's side, Sarri has been forced to give Emerson Palmieri some Premier League minutes. While there hasn't been too much proof that this will solve the defensive struggles, it's gotten to the point that many supporters are on board with this decision.
The combination of the supporters' frustration and Sarri's apparent distrust of Alonso lends itself to one conclusion - if he is not going to improve his defensive abilities he needs to be sold once the summer window opens in favour of a better defensive option.