Martin Kelly has been ruled out until 2013 after it was confirmed the Liverpool defender has ruptured the anterior cruciate ligament in his right knee.
The England international had feared the worst after limping out of Sunday's defeat by Manchester United and tests have now revealed the extent of the problem.
Kelly will undergo a reconstruction process of his ligament which Liverpool say will require a 'significant period' on the sidelines.
The defender's absence is another setback for boss Brendan Rodgers, who has yet to win in the Premier League since taking over at Anfield this summer.
Rodgers has also been hit by the injuries suffered by Daniel Agger and Fabio Borini in the 2-1 loss to United, which also saw Jonjo Shelvey sent off.
Agger sustained 'a significant bone bruise to the left knee' and, although there is no ligament damage, further tests will be required to discover when he will return to full fitness.
Italian forward Borini has 'considerable swelling' to his right ankle but an X-Ray did not find any fracture.
The summer signing will undergo an MRI scan on Tuesday to assess any soft tissue damage and determine when he may be able to return to playing.