Marcos Alonso's biggest mistakes this season  (VIDEO)

Marcos Alonso has been of the best in the world in recent seasons, however, his form has dropped off massively this campaign. Back in September, Chelsea boss Maurizio Sarri was glowing in his praise for the 28-year-old. “Alonso, at the moment, [in] this position at left-back is maybe the best in Europe,” Sarri said, per the Independent. “Physical qualities at a top level, I think. "He’s doing very well in the offensive phase. But I also think he can improve in the defensive phase. If he improves that, he could be the best left-back in the world." However, since then, Alonso’s form has been in free-fall. Chelsea fans has made a video of Alonso’s biggest mistakes in recent months and it’s gone viral.