Barcelona have told Liverpool they will meet the release clause in striker Luis Suarez's contract.
The clause is understood to be about £75m, and Liverpool are not prepared to sell the 27-year-old for less.
After "productive" talks with Barcelona this week, the Reds are trying to establish if Chile forward Alexis Sanchez will move in part-exchange.
Uruguay international Suarez is serving a four-month ban for biting Italy's Giorgio Chiellini during the World Cup.
Barcelona are willing to include Sanchez as part of the deal, but if the Chile forward opts to stay, Liverpool are prepared to sell Suarez in a straight deal.
Suarez, who joined the club for £22.7m from Ajax in 2011, has four years remaining on his contract at Anfield.
Liverpool chief executive Ian Ayre spent much of Wednesday in discussions with senior Barcelona officials in London.
"The talks held were productive," a senior Liverpool source told BBC Sport. "There are sensible expectations on both sides.
"Further talks and discussions will take place but no deal has yet been finalised."
Barcelona club president Josep Maria Bartomeu said on Wednesday: "This year we are going to restructure the team in depth and we are working on that.
"We have been working on that since February, but I can't reveal things we are doing.
"We have to be discreet - we can't give clues to other teams.
"We do have a lot of negotiations at a very advanced stage, but the World Cup is going on. People are speculating about a lot of players at the World Cup, but there's a lot of different factors."
Asked about Suarez, he said: "He's a great player, a global star and we want him to play as well as he's playing up to now. I'm speaking as a football fan.
"He's a player who needs to rebuild himself and get back to playing football."
Suarez apologised on Monday for biting Chiellini, after which Barcelona sporting director Andoni Zubizarreta said: "Suarez has shown he is humble enough to admit an error, which is very important.
"Everyone knows Luis is an excellent player, everyone knows last season he played in various positions in attack, but everyone also knows he is a Liverpool player."
Bartomeu described the player's apology as "honourable" and "good for football".
"He did something wrong and it's everybody in football's responsibility, whether it's Liverpool or others, to help him to go ahead and press on with his football career. It's not easy to admit your mistakes," Bartomeu said.
Croatia midfielder Ivan Rakitic, who completed his move to Barcelona from Sevilla on Tuesday, said: "The fact he has had the character and the strength to go in front of everyone and say sorry says a lot about him as a person."