Coutinho moved to Barcelona from Liverpool in January 2018, the Reds receiving a transfer fee that could hit €160million (£142m) with add-ons.
He initially appeared to be a good fit, producing some solid performances in his first few months at Camp Nou as he finished the 2017-18 season with eight goals in 18 LaLiga matches.
But he flattered to deceive last term, netting only five times in 22 league starts as he failed to live up to expectations.
He has been linked with a transfer to United, with Barca said to be eager to free up funds to sign Neymar, but his agent effectively ruled out such a move.
"Manchester United is a great club, I have players there and I have all the respect for them, but as far as Philippe goes, it would be an extremely difficult to a near-impossible move," Joorabchian told talkSPORT.
"I would be very difficult for Philippe to play for any of Liverpool's rivals, because he has such a great affinity towards Liverpool. His time there was fantastic.
"Like all big players at some point you want to experience a different thing in your career because your career is very short, but it [his Liverpool exit] has no reflection on the fact his heart and affinity is very much with Liverpool.
"I know he was cheering every time they had the chance. Lucas Leiva is the same way. A lot of these guys who leave Liverpool remain Liverpool fans because of the fans and the passion they have.
"So, it would be hard for him to go to a rival. Every time we've spoken about it we've had that same conversation, he would find it hard to play for another club in the Premier League."
Coutinho has also been tentatively mentioned as a potential target for the Reds, though Joorabchian doubts a return to Anfield will materialise.
"The thing is, Liverpool have built a tremendous squad," he said. "The manager has a great balance there and it's probably one of the best run football clubs in the country.
"So, with the build-up they've done and the squad they have, it [bringing Coutinho back] would really have to be something they would have to decide, whether or not they feel there is now a gap in the squad for someone like Philippe.
"I think it's going to be a very difficult deal, but most of the big ones are always very, very difficult.
"Obviously, if he were to move back [to the Premier League], it would have to be Liverpool, but at the moment I think it would be difficult and it would be up to them."