Coutinho has been Liverpool’s stand-out player this season with nine goals and six assists in the Premier League.
And his form has seen him linked with Barcelona with international team-mate Neymar publicly calling on him to join him at the Nou Camp.
Barnes wants Liverpool to fight to keep him, but says the club should only keep players who want to be there.
“He’s very important,” Bonus Code Bets ambassador Barnes told Express Sport.
Philippe Coutinho has been tipped to leave Liverpool this summer Liverpool players tribute to Hillsborough disaster victims Sat, April 15, 2017
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“He’s our talisman in terms of creativity. I think he’s probably been a bit burdened at times because he’s the one who we really rely on to create.
“We have helped him out now Firmino has come and of course we’d like him to stay.
“You want to keep your best players but modern football is such that players come and go.
“I want players to stay at Liverpool who want to stay. I want him to stay, but if he doesn’t want to stay you can’t force him because that’s modern football.
John Barnes believes Liverpool face a fight to keep Philippe Coutinho
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“So I would love him to stay and we have to try and keep our best players but if he decides to go, as much as it may not be his decision it may be Liverpool’s decision, we’ll have to try and replace him.
“But of course I’d love him to stay.”
But Barnes wouldn’t be drawn on how much it would cost to prise him away from Anfield.
“Not a clue,” Barnes said when asked how much Coutinho would cost.
“I don’t know anything about fees but it’d be a lot of money. He’s going to be very expensive.”