Liverpool's Virgil Van Dijk will be out for a lengthy period after damaging his anterior cruciate ligament in Saturday's Merseyside Derby with Everton.
The Dutch defender was involved in a collision with Toffees goalkeeper Jordan Pickford in the first-half of the 2-2 draw at Goodison Park.
A Liverpool statement read: 'Van Dijk was required to be substituted and further assessment on the injury has revealed an operation will be needed.
'No specific timescale is being placed upon his return to action at this stage.
'Following surgery, Van Dijk will begin a rehabilitation programme with the club’s medical team to enable him to reach full fitness as soon as possible.