Van Dijk will undergo surgery on the ACL problem, and it remains to be seen whether he will feature again before the end of the campaign.
"If it was an ACL (anterior cruciate ligament) and without any impact, this injury happens quite a lot, where there is no-one around the player and he twists and all of a sudden he has done his ACL, then that's fine," he told talkSPORT.
"You can say he might be back in seven months and might be a similar player.
"When it's an impact injury, which this was, you're talking the ACL, which potentially could have damaged his PCL (posterior cruciate ligament) and could mean the tibia and the fibia banged together.
"If it is any of them, and not just the ACL, then this could be a lot longer for Virgil van Dijk to come back I would doubt that we are going to see the same level of Virgil van Dijk when he comes back."