That is according to ESPN correspondent Sam Marsden, who claims Nou Camp bosses could cut their losses if they receive an offer worth £100m.
Coutinho joined Barcelona from Liverpool for a club-record £142m in the January transfer window of 2018.
He initially impressed but has found the going difficult in his first full season with the Catalan club.
Marsden said: “The longer this goes on the more feasible that Barca would accept an offer.
“The problem is they paid so much for him, and have invested so much into him, that they don’t want to take a big hit.
“At the moment the official line is he’s not for sale.
“But unofficially there are whispers that if Manchester United, Chelsea, Bayern Munich or whoever it may be, came in during the summer and tested Barcelona with a bid, maybe of around £100m, then maybe the club would think now is the right time to cut their losses.”
In other Liverpool news:
It has been suggested Liverpool could look to bring Coutinho back to Anfield after missing out on Nabil Fekir last summer.
But Marsden would be surprised if Barcelona opted to sell the Brazilian back to his former club.
He told the Liverpool Echo’s Blood Red podcast: “As for Liverpool, I don’t have any insight from their point of view, but if they did come in with a bid it would almost be like Barca would be put off by selling him back to the club where they bought him from.
“Even if Liverpool were to match the same price that another club was prepared to pay, it almost feels like Barcelona would have been had off.”
Liverpool boss Jurgen Klopp previously shot down the idea of re-signing Coutinho.
When asked about the potential of a deal in January, Klopp said: “I would not say it is a potential transfer or a likely one.
“Nothing to say. Whatever I say would open more stories and there is no story.
“Phil is at Barcelona and as I know he fits really well and everything is fine.”