Earls picked up the problem in an unfortunate clash with Edinburgh wing Dougie Fife as Munster ran in six tries in a 38-6 triumph at Thomond Park. The 26-year-old, who has just signed a new contract with the province and the Irish Rugby Football Union, has since had a scan to assess the damage and has also seen a specialist to confirm the prognosis.
An eight-week absence would see Earls return to action just a fortnight before Munster host four-times Heineken Cup kings Toulouse in Limerick on the weekend of April 4/5/6.
"Keith Earls has been ruled out for approximately six to eight weeks after sustaining medial ligament damage to his left knee," read a statement from Munster.
"Earls was scheduled to join his Irish colleagues in camp on Sunday evening after Munster's Round 6 Heineken Cup game versus Edinburgh. But, after picking up an injury to his left knee, he was replaced after 25 minutes and consequently did not travel to Carton House."
As well as leaving him with plenty of hard work ahead if he is to be back to his best for the resumption of continental competition in the spring, the injury is likely to force Earls to sit out the entire RBS 6 Nations campaign for Ireland.
The wing cum centre cum full back missed the autumn internationals with knee problems and he could now repeat that absence in new coach Joe Schmidt's first tournament in charge. Ireland's final game comes against France on March 15, a day short of eight weeks since Earls picked up his latest setback.