The Barcelona star left Anfield for £142million in January 2018 but he has struggled to settle in at the Nou Camp.
Coutinho was whistled by his home supporters in Barcelona's 3-1 victory over Rayo Vallecano on Saturday.
Lionel Messi and Luis Suarez continued to thrive as Ernesto Valverde's side came from behind but Coutinho was dragged off with 10 minutes to go.
His replacement, Ivan Rakitic, set-up Suarez moments after replacing the former Liverpool man.
Now the Brazil international has appeared to have had enough, as he has told friends he wants to leave and has spoken to Manchester United players about a switch to Old Trafford according to the Mirror.
Coutinho is believed to miss the Premier League but knows Jurgen Klopp's side are unlikely to want him back. The ex-Liverpool midfielder reportedly refused to train the summer prior to signing for Barcelona. The Catalan giants eventually got their way with persistent pestering and the Reds were forced to sell their talisman in the winter window.
It is also suggested Reds sporting director Michael Edwards insisted on a clause that meant Barcelona had to pay a premium if they were to try and sign another Liverpool star.
This has caused tensions between the two clubs which makes a return to Anfield for Coutinho problematic.
United is thought to be his preferred destination but Ole Gunnar Solskjaer's team are not the only club interested in his services.Ligue 1 champions Paris Saint-Germain are also said to be interested having wanted Coutinho whilst he was at Liverpool.
Barcelona pipped Thomas Tuchel's side to his signature last year and with the La Liga side beating PSG to the signature of Frenkie De Jong, they reportedly want revenge.
Coutinho has scored eight times and set up his team-mates five times in 38 appearances in all competitions this campaign.