The former United star spoke on BBC 5 live Sport after the Blues lost 3-0 to Roma on Tuesday and believes they made a big mistake letting the midfielder go:
His £40 million transfer raised some eyebrows in the summer, and it was indeed a surprise that Chelsea allowed him to join a direct title rival.
Blues boss Antonio Conte appeared to want to keep the Serb, after telling Sky Sports (h/t Samuel Lovett of The Independent) "sometimes you must accept different decisions, but he is a great loss for us."
Director Marina Granovskaia and technical director Michael Emenalo wield much of the power at Stamford Bridge when it comes to transfer activity, so it is perhaps they who bear responsibility for the decision to sell Matic to United.
Football journalists Adam Bate and Kristof Terreur also believe it was a misstep from Chelsea:
Indeed, the Blues have missed the stability he provided in midfield, and his absence has been even more keenly felt because of N'Golo Kante's struggles with injury this season.
That was on display against Roma, as the Giallorossi tore them apart at the Stadio Olimpico.
Neither of Chelsea's summer recruits, Tiemoue Bakayoko and Danny Drinkwater, are in the same mould as Matic, and both have had difficult starts to their Stamford Bridge careers—the former has struggled to replicate his Monaco form, while the latter has largely been sidelined through injury.
What's more, Matic has been free to put in excellent performances for United as he did against Tottenham Hotspur, per Sky Sports Statto:
Sky Sports' Kaveh Solhekol believes the Blues do not deserve too much criticism after their defeat in Italy:
However, while Alvaro Morata looks to be a strong replacement for Diego Costa, Matic's departure was a problem of their own making.
Conte should be able to bring more balance to Chelsea's side when his full complement of midfield options are available, but it's clear their decision to sell Matic was a poor one, and they may need to make amends in January.