Coutinho, 25, has been of interest to Barca for a number of months and Ernesto Valverde's men have stepped up their efforts to bring him to the Camp Nou this summer, with the future of Neymar also up in the air.
Liverpool are understandably desperate to keep Coutinho, who signed a long-term deal with the club earlier this year, and have placed a £133.7m [€150m, $175.7m] price tag on their coveted playmaker in order to ward off Barcelona, who are also said to be interested in Kylian Mbappe.
Coutinho featured and scored a brilliant goal during the Reds' victory of the Premier League Asia Trophy last week, but Barnes was worried by his body language on the pitch and is concerned he may be thinking of a fresh challenge with Barcelona.
"You could tell by the way he reacted after he scored, with no celebration or anything, that something isn't quite right with Philippe at Liverpool," Barnes told ESPN.
"It would be great if Liverpool keep him, but if he goes, I wish him all the best. Jurgen Klopp still has a good squad, so he will maximise the potential of the squad without Coutinho. We'd like him to stay, but if he goes Klopp will still find a way of being competitive."
Coutinho's protracted move to Barcelona is the latest transfer saga that Liverpool have had to contend with this summer. Klopp's side have been heavily pursuing Southampton captain Virgil van Dijk and RB Leipzig midfielder Naby Keita with little success, but Barnes does not think the Reds need to sign more players this summer.
"The Klopp factor is incredible at Liverpool because the fans support him, no matter what he does, no matter who he signs," Barnes added.
"If he can get Van Dijk or Keita, all well and good. But we're not hanging our hat on the fact that we need more signings. If they come, it's positive. If they don't come, in Klopp we trust."