"I think the outcome of the play-off could have a knock-on to Coutinho," Thompson told Sky Sports.
"If things go pear-shaped then he has a pretty good excuse to say: 'Let me go, I want to play in the Champions League. ' It is even more important in that respect.
"If we get through to the group stages then I think the owners - because they put everything at Coutinho's disposal before, giving him a five-year deal and the pay increase that he and his agent asked for - have strong enough grounds to stand firm.
"The owners know it's Barcelona but to them it's a contract signed and until they've got a player who can fill his boots then they have no interest in selling, especially after the way the club was embarrassed with the timing of the transfer request."