Chelsea will be without key defender Levi Colwill for an extended period of months after he injured his knee in training.
The England international, 22, damaged the anterior cruciate ligament of his knee on Monday and could miss most of the season.
“We know each other from last year and, you know in our way, how important Levi has been,” boss Enzo Maresca said.
“I spoke with him yesterday and I told him that if we achieve what we achieved last year, it is also because of him – and he was a main player for us.
“It (the injury) was in the first session on Monday, just in the last minutes of the session.”
Chelsea have already signed cover at left centre-back after signing Jorrel Hato from Ajax for around £37m.
Chelsea play Bayer Leverkusen in a friendly on Friday.
