Claudio Ranieri believes his former side Chelsea’s struggles have at least been partly been down to the departure of Diego Costa.

Though the Spanish international will formally return to Atletico Madrid in January, Costa is training with his new club and will not play for Chelsea again after the two sides agreed a transfer worth up to £57.2million.

Chelsea boss Antonio Conte had informed Costa that he had no place in his plans at the end of the season and opted to sign Alvaro Morata as his replacement.

The former Real Madrid striker has adapted swiftly to life in the Premier League, scoring seven goals in 12 appearances. There have been times, though, when Chelsea appear to have missed the feisty, tempestuous presence of Costa, most notably in a 0-0 draw with Arsenal last month where Morata was unable to outmuscle the Gunners’ backline in the same way his predecessor had.

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Ranieri, who managed the Blues between 2000 and 2004, believes Conte’s side are still adapting to playing with Morata. 

He told Corriere dello Sport: “What has Chelsea’s problem been so far? It’s down to the injuries and the changes in the squad. It’s not easy to go from Diego Costa to Morata.

“The first is a leader, he carries the team on his shoulders and plays with anger, with force and sheer will. The other is more of a dribbler.

“When you change your centre-forward, you have to also change your approach.”

Morata’s future had been the subject of surprise speculation on Monday when he seemed to suggest in an interview with an Italian newspaper that he regretted moving to London. But speaking at a press conference later that day insisted he was so happy at Chelsea he would be willing to stay for 10 years.