Chelsea defender Ben Chilwell has suffered a “bad” hamstring injury with no timescale yet put on his return, says Blues boss Mauricio Pochettino.
Chilwell has had a scan on the injury that forced him off late on against Brighton in the EFL Cup on Wednesday.
Chelsea are already without Reece James until after the international break with a thigh problem.
“When they’re at their best, they are the best full-backs in the world,” said Pochettino.
“At all clubs, important players are missed when they don’t play.
“If the question is ‘do we miss them?’ Of course. Reece is a top player and [Chilwell] also.”
Chilwell missed three months last season with a hamstring problem, limiting him to just 23 Premier League appearances. James meanwhile played just 16 times in the league because of knee, thigh and hamstring problems.
Marc Cucurella, Levi Colwill and Axel Disasi are the contenders to play at full-back in Monday’s Premier League trip to Fulham, but Pochettino says no-one in his squad can fully replicate what his first-choice full-back pairing brings.
“All teams when they miss important players are affected [in their] performance,” added the former Tottenham manager.
“Why did we not sign another Ben Chilwell and another Reece James? Because there’s only one Reece James and one Ben Chilwell.
“If you have in the squad one top player in one position, it’s difficult to bring in another one in the same position to sit on the bench. It’s about balance.”