Steven Gerrard has urged Liverpool to do everything they can to sign Virgil van Dijk from Southampton this summer.
Liverpool were interested in Van Dijk earlier this summer before they released a statement apologising to Southampton amid tapping-up allegations.
The centre-back is keen to leave St. Mary's this summer after handing in a transfer request, but Southampton maintain he is not for sale.
"Yes [Van Dijk is a necessity]," former Liverpool captain Gerrard, now an academy coach at Anfield, said in his role as a BT Sport pundit. "For me, if you want to compete in the league and in the Champions League [Van Dijk is needed].
"It's been well documented that we need two or three signings in."
After publicly expressing his desire to leave the club, Van Dijk has not featured in Southampton's first two matches of the season.
Despite Southampton closing in on the signing of Lazio's Wesley Hoedt, manager Mauricio Pellegrino recently said he wanted keep Van Dijk.
When asked if he wanted to add another centre-back to his squad even if Saints retain Van Dijk, Pellegrino replied: "Yes, because as you know right now it's the position that we are in disadvantage.
"I think it's an area where we can improve with another player.''
Meanwhile, Southampton chairman Ralph Krueger has explained why the Premier League side have taken their firm stance on the Netherlands international.
"It's about an overall much, much, much bigger picture -- a change of course for Southampton," he said. "We want to mature, we want to be a team that can profit from synergies that create a much more attractive football and a better product for the fans, and gives us a chance to get back into Europe.
"That's one player in this whole equation of 25 and it is the visible one, but for us it's the principle and it's the path and it's the statement we need to make to get to a new space as a club.
"We are very, very adamant about carrying this through."
Liverpool have routinely signed Southampton's best players in recent years, with Sadio Mane, Adam Lallana, Nathaniel Clyne and Dejan Lovren all making the switch from St. Mary's to Anfield.