The Catalan giants, who recently sold Neymar for a fee thought to be around £200m, have reportedly had a £72m bid for Coutinho and an offer in the region of £80m rejected by the Reds.
The 25-year-old missed Saturday's Premier League opening 3-3 draw with Watford due to a back injury, and he has not travelled with the squad for tonight's Champions League first leg qualifier against Hoffenheim.
Twitter account @BrazilStat has quoted Firmino as saying: "I prefer to not think of [Coutinho leaving] because it'd be awful. He's a great player but also a great friend to me."
The former Inter Milan star, who joined Liverpool in 2013, was best man at Firmino's wedding earlier in the summer.