Following the departure of Neymar to Paris Saint-Germain in a world-record €222m (£198m) deal, Barcelona identified Coutinho as a replacement for the 25-year-old.
With the player reportedly interested in joining the Nou Camp, Liverpool have most recently rejected a second bid from the Copa del Rey champions worth a reported €100m (£90.3m).
While Reds manager Jurgen Klopp previously reiterated his stance that the Brazilian would not be leaving Anfield, Bellamy is doubtful on whether his old side can hold on to the former Inter player and claims it will be "nigh-on impossible" for Coutinho to turn down the chance to play for La Blaugrana.
"Liverpool are going to stay firm, but it's still early in the transfer window, and how long can they stay firm for?" Bellamy told Sky Sports. "No supporter wants to hear this, everyone thinks their team is the biggest, and rightly so, but this is Barcelona. If they come calling, it's very difficult for players to turn down."
"This is Coutinho, who has the opportunity to play with Lionel Messi, the best player to play football, to go to one of the best clubs in football. How can you look him in the eyes and tell him this isn't an improve [sic] him? To tell him this isn't what you deserve?
"This is the difference. With Liverpool you've got the chance of competing in the Champions League with Liverpool, or there's a chance of realistically going to win the Champions League with Barcelona. It's nigh-on impossible to turn them down."
Coutinho last featured for Liverpool in pre-season on 1 August and is doubtful for the club's league opener against Watford on 12 August, putting more speculation on his future.