Lucas looking at two-month lay-off
Press Association Sport understands the Brazil midfielder has damaged the medial collateral ligament in his right knee.
Although not as serious as injury to a cruciate ligament - the 27-year-old ruptured the anterior cruciate ligament in his left knee in November 2011 - it will still keep him out for six to eight weeks, which would take him into March.
Lucas sustained the injury just 20 minutes after coming on as a half-time substitute in Saturday's 2-2 draw at home to Aston Villa.
He told manager Brendan Rodgers he heard 'a click' in his knee following a challenge with Fabian Delph and subsequently left the ground on crutches, later tweeting: "It is in God's hands."
Lucas had been left out of the starting line-up as Rodgers opted to play captain Steven Gerrard in a holding role for the second successive match, allowing him to field a more attacking side with returning striker Daniel Sturridge accommodated at the Brazilian's expense.
The experiment did not work and Rodgers corrected his mistake at half-time and Lucas' arrival did allow the Reds to regain some control.
With Liverpool looking to hold onto fourth place in the Barclays Premier League, Rodgers could be tempted to find additional cover in the transfer window as he has been short in the area of defensive midfielders for some time.
Meanwhile, Liverpool defender Sebastian Coates is set to rejoin former club Nacional on loan as he battles to be fit for this summer's World Cup.
The 23-year-old has been sidelined since tearing an anterior cruciate ligament in a knee while on international duty for Uruguay in August.
Coates is still continuing his rehabilitation but Press Association Sport understands he is already in Montevideo awaiting completion of the move.
Liverpool are prepared to allow the centre-back to continue his rehabilitation in his homeland with a view to him regaining fitness and being able to get some match practice before this summer's tournament in Brazil.
"It would be beautiful to join Nacional and complete my recovery in Uruguay with my family and friends," the centre-back told Radio El Espectador 810.
"The negotiations can be hard sometimes, and we have to wait a bit."
Coates joined Liverpool from Nacional in August 2011 in a reported Â£7million deal but struggled to force his way into the first team.
The centre-back has made just 24 appearances in that time, half of which have been in the Premier League, and scored two goals.
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