During their fourth Group A fixture against the French champions on November 6, the Senegal international came off the bench to win a penalty for his side, who were trailing.
He was not the designated penalty taker, but he stepped up with the ball and his effort was easily saved by PSG goalkeeper Keylor Navas.
After the match, Diagne was dropped and fined by coach Phillip Clement, and he was never summoned for games until the Belgian First Division A came to an early conclusion a week ago.
The 28-year-old, who joined the Blue-Black on a season-long loan from Galatasaray last summer, narrated his torrid experience at Club Brugge despite returning four goals in nine matches across all competitions.
“I apologised to the players and the manager but I was banished,” Diagne told the Guardian.
“I came in and trained my hardest every day but was never called for the matchday squads. He was picking players ahead of me whom I respected but who, honestly, weren’t at the same level as me.
“After a while I went to the manager and asked what was going on and he just said: ‘I make the decisions, I’m the boss.’ After that he just ignored me.
“For my last three months at Brugge he didn’t say a word to me, not so much as a ‘hello’. I think he never wanted me in the first place.
“It was other people at the club who had persuaded me to go there. I think he took advantage of my penalty miss to make a point.”
After Club Brugge’s coronation as champions of the Belgian top-flight this season, Diagne’s image was omitted from their celebration graphic.
The Senegalese, in a hilarious reaction, edited the design and put his face in place of the coach’s.
He is expected to return to Galatasaray where he has three years left on his contract, but he is uncertain about his future with the Turkish Super Lig giants.
“I’m very happy to play for them but I don’t know if they intend keeping me. I haven’t spoken to them yet,” he said.
“Some people say they need to get some big earners off the payroll but I don’t know who that means. If they decide they need to sell me, then I’m sure I’ll find somewhere that suits my style.”
During his stint at Kasimpasa before moving to Istanbul in January 2019, Diagne – who won the Turkish Super Lig top scorer award last season – struck a fine partnership with Egypt’s Mahmoud Trezeguet Hassan.
“We talk regularly and he keeps saying I would thrive in England,” he added.
“I’m big and strong, I can hold up the ball and lay it off, I’m good in the air and I’m a finisher. All I know is that, whether at Galatasaray or somewhere else, I am eager to get back playing and scoring again.”