Dembele has had a mixed first season in Catalonia and has even been linked with a move away from Barcelona after rumours suggested the board weren't happy with his behaviour.
The speculation comes as no surprise for Weidenfeller who spoke to 'GOAL' about the young forward's departure from Dortmund.
He said: "Dembele had the chance to make a name for himself at Dortmund when he was only 19. Here he became the player that Barcelona wanted to buy.
"Instead of being grateful though, Dembele left the club, stayed at home, attacked it and abandoned his team-mates. He was acting without manners, in bad style".
To force a move through to 'Los Cules, Dembele declared himself in rebellion, something that has not been forgotten in Dortmund.
Weidenfeller continued: "When he left, he didn't even pick up his boots, it's ridiculous. These are not ways to leave a place because you feel uneasy. Football is a team sport, it's not tennie or any other individual sport.