Chelsea captain John Terry is set for up to three weeks on the sidelines after suffering a muscle injury.
The centre-back only recently returned to action after shaking off an ankle problem he sustained against Swansea City in September.
Terry has been limited to six minutes of Premier League action since, though he did play the entire game in Chelsea's EFL Cup defeat to West Ham last month.
The 35-year-old featured for Chelsea's Under-23 side on Monday, but will now not be available for at least the next fortnight.
Speaking ahead of Saturday's meeting with London rivals Tottenham, manager Antonio Conte said: "For tomorrow Terry and [John Obi] Mikel aren't available.
"John has a muscular problem and Obi will train with us again next week.
"It's a pity [for Terry] because he recovered well from his last injury and now he has to start again."
Winger Willian has not featured for Chelsea since the win at Southampton last month.
The Brazil international has been linked with a reunion with Jose Mourinho at Manchester United.
But Conte said: "Willian has come back, now it's important to find good form because in this period he was unlucky.
"It's important now to be focused on the work, Willian is an important player for us and I count on him a lot."