Chelsea midfielder Frank Lampard and defender Branislav Ivanovic will be out of action until the end of January.
Boss Jose Mourinho confirmed the news after Chelsea's impressive 3-0 victory over Southampton on New Year's Day, which they both missed.
Both men picked up injuries during Sunday's 2-1 win over Liverpool.
Serbia defender Ivanovic suffered a knee injury and was substituted in the first half, while England international Lampard sustained a muscle injury and did not come out for the second period.
They will miss Sunday's FA Cup third round tie at Derby County and league games at Hull City and at home to Manchester United and West Ham United later this month.