Chelsea fear captain Reece James is facing another long-term spell out.
James suffered a hamstring injury in defeat at Everton Saturday, having only returned recently after suffering a similar setback in the opening game of the campaign.
The fullback, 24, could risk sitting out for up to three months, as he needs to see a specialist to solve the problem.
According to the London Evening Standard, it is James' seventh hamstring injury in three years.
This season there have been just eight appearances in the Premier League.