The Dutchman was a surprise omission from a strong-looking line-up for the Reds at the Emirates Stadium.
And This Is Anfield understands that his absence is down to illness, rather than any decision to rest him.
The captain is sure to be missed as Liverpool look to secure passage to the fourth round at the expense of a fellow title challenger.
Speaking to BBC Sport, Jurgen Klopp confirmed: “Virgil is ill. We were actually kind of lucky in the last two or three weeks.
“Virg got a virus, we have to see tomorrow if he is OK for the next one. But for today, for sure, he is not.”
Van Dijk has made 20 appearances in all competitions this term, making a welcome return to his best form after a shaky 2022/23 campaign.
There is no established centre-back on the bench, with Nat Phillips not involved despite his loan spell at Celtic ending this week.
It is a young reserve group with an average age of 20.4, including 16-year-old midfielder Trey Nyoni for the second time this season.