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The Chelsea manager, Maurizio Sarri, whose side play Arsenal tomorrow. Photograph: Chris Brunskill/Fantasista/Getty Images

Mauricio Sarri has admitted Alvaro Morata is still suffering from a crisis of confidence, even if the Spain forward is likely to start tomorrow’s London derby against Arsenal.

Morata, who was Chelsea’s record signing when he joined from Real Madrid for around £58m last summer, has scored only once in the top flight since Boxing Day. He began last weekend’s 3-0 victory at Huddersfield with Olivier Giroud not yet deemed match fit following his late return after the World Cup.

Morata, prolific in his first few months at Stamford Bridge, had suffered back problems over the second half of last season, but is now fully fit and, apparently, simply in need of a goal to restore his form. “I’m not worried about Morata,” said Sarri. “He is a very great player. I think that, in this moment, he needs only to gain confidence. But he is a great player.

“Maybe, maybe [his confidence is low]. He needs to score. As all the strikers in the world do, I think. He needs to gain confidence, but he’s improving so I’m not really worried about him.”

Chelsea will be without the injured Cesc Fabregas against Arsenal, while Mateo Kovacic - signed on loan from Real Madrid - will only be able to feature from the bench. “He’s a very technical player but, in this moment, he has to work,” added Sarri. “I think he’s not ready now for 90 minutes, but maybe he could be used for the last 30 minutes. I expect a lot from him because, for me, he’s a very great player.”