Bissouma posted a video on the social media platform Snapchat last weekend in which he inhaled a balloon believed to contain nitrous oxide, commonly known as laughing gas.
Spurs launched an internal investigation and while Bissouma apologised for his “serious lack of judgement”, he was banned for one match and will miss Monday’s away game at Leicester.
Nitrous oxide was reclassified as a Class C drug last year under the UK Government’s Anti-Social Behaviour Action Plan and its possession for recreational use is a criminal offence.
Postecoglou has left the door open for the Malian international to establish himself as a key figure again, but he still has bridges to build.
“He has responsibilities, responsibilities towards the club, his teammates, our fans and everyone associated with the club, and he has failed to fulfil these responsibilities,” said Postecoglou.
“There must be sanctions for this. He will not be available on Monday. We have suspended him for the game on Monday.”
“In addition, trust must be built between Biss and me and between Biss and the group.
“He’s going to have to work hard from now on to get that back, and it’s not about just one game. He might get a one-game suspension, but he’s going to have to earn it.”
“The door is open for him and hopefully we can help him realise that his decisions affect more than just himself and enable him to make better decisions in the future.”
When asked what Bissouma should do next, Postecoglou answered clearly, although this was not his first misjudgment after two red cards last season.
He added: “Behaviour, mate. It’s very simple. He makes better decisions and behaves better in the future. He is obviously disappointed and has apologised profusely, not only to me but to the club and everyone involved.”
“That’s just the first part of the process. The next part now is behavior. Making sure that, like I said, he’s doing the things he needs to do.”
“We all make mistakes and it’s how you fight back from those mistakes that counts and what you do is much more important than what you say.”
Tottenham remain active in the transfer window, despite the arrival of striker Dominic Solanke last Saturday in a deal that could be worth £65 million.
Exits are a top priority and the club is ready to approve the departures of Sergio Reguilon, Giovani Lo Celso and Manor Solomon.
In addition, a number of young players such as Ash Phillips and Alfie Devine could leave the club on loan, and Jamie Donley is close to a temporary move to Leyton Orient.
However, 19-year-old striker Will Lankshear is expected to remain part of Postecoglou’s first team after an excellent pre-season.
