The Brazil international has only spent a little under 18 months away from Anfield.
He swapped Merseyside for Catalunya in January 2018, with a big-money transfer pushed through at the end of a protracted saga.
Coutinho was expected to slot seamlessly into the fold at Camp Nou, but he has struggled to make the desired impact.
The ex-Reds defender told Sky Sports: “I would take him back in a heartbeat, but it would have to be now.
“You don't want to leave it another 12 months, I think he still has the ability.
“He's suffered at Barcelona. We've seen him playing out wide on the left, but he's not Neymar.
“He likes to be in the middle where he can pull strings and is getting on the ball to hurt teams.
“He doesn't do that and he's not a left-winger and that's where he's playing at Barcelona; they don't love him like Liverpool loved him.”
It is suggested that there could be a “buy-back clause” in the deal that took him to Barca, and Thompson added: “He was that little bit clever, that creativity behind those front three that you could go to in games where you knew you were going to have the majority of the possession.
“He could open that door, he could score the goals that would get you the win.
“I would have him back, I don't know about the football club, but he is the one with that ability.
“Knowing our club, we've been very shrewd, maybe there's a buy-back clause in there for maybe less than half what we sold him.”
Coutinho made 201 appearances for Liverpool between January 2012 and the winter window of 2018.
He recorded 54 goals and an impressive number of assists and it has been suggested that Jurgen Klopp, who has seen his side fall agonisingly short in their Premier League title bid, has been unable to replace the South American’s creativity since seeing him depart.