Chelsea boss Antonio Conte never should have sold Diego Costa, claims former Blues midfielder Deco.

Costa left Chelsea last summer to rejoin former club Atletico Madrid after publicly falling out with Conte during the Blues title winning campaign of 2016/17.

And Conte and co’ struggled to replicate that championship winning form last term, with Costa are sorely missed figure at the spearhead of Chelsea’s attack.

Alvaro Morata, who was signed as a direct replacement for Costa, failed to produce consistent goals for the West Londoners – managing only 11 in the top flight following his £58 million move from Real Madrid.

And while Olivier Giroud, who joined Chelsea in January, gave a much needed boost to the Blues strikeforce, the Frenchman’s goals were unable to stop the Blues from finishing outside the top four for the second time in three seasons.

Deco believes Antonio Conte’s failure to sufficiently replace Costa last summer is what cost the Italian’s side the Premier League last season, and ultimately, what could cost him his job at Stamford Bridge.

“The Premier League over the last few years has become more competitive. There is a lot of big teams, a lot of replacements,” Betfair ambassador Deco told Express Sport.

“I think we will see changing winners in the next years. Manchester City, they did something not normal in the Premier League.

“But Chelsea they won last season and for me they lost one important player like Diego Coata, that’s my opinion.

“The way they play, Diego was very important for them. It was difficult to find a substitution. Morata is not the same, even Giroud is not the same. Diego was for me the perfect player for the way Conte played.

“I think they lost [Nemanja] Matic too, they had good midfielders but I think for me it was Diego Costa [leaving].”

Conte is widely expected to leave Stamford Bridge this summer after a disappointing campaign, with both Maurizio Sarri and Luis Enrique being eyed as potential replacements for the Italian.

Chelsea however are yet to comment on the situation, and will now leave any decision over his future until after the World Cup, which starts tomorrow.