Lucas sidelined for rest of season
Lucas was carried off on a stretcher in the second half of the 2-0 victory at Stamford Bridge and subsequent scans have revealed damage to his left anterior cruciate ligament.
"The Brazil international will undergo surgery and unfortunately be ruled out for the remainder of the current campaign," Liverpool said in a statement on Thursday.
The holding midfielder, who joined the club from Brazilian team Gremio in 2007, had started 12 of Liverpool's 13 league matches this season.
"I'm having a wonderful time at Liverpool that unfortunately will be interrupted because of this injury," Lucas, 24, said in a separate statement.
"I have never suffered an injury as severe as this. It was a blow to discover I will be out until the end of the season but I will fight to get back as soon as possible."