The Mali international has been a key man for Graham Potter's team for the last two seasons but the 25-year-old is on the cusp of a £25m move to Tottenham.
Bissouma will have a medical at Spurs later this week but the Seagulls have been preparing for his exit for some time.
His departure could allow the likes of Alexis Mac Allister, Jakub Moder, Enock Mwepu, Moises Caicedo and Steven Alzate to nail down that central midfield slot.
Brighton will however be keen to keep their playmaker Leo Trossard. The Belgian was impressive last season and is wanted by new Man United boss Erik ten Hag at Old Trafford.
Trossard is in the final year of his contract and any bid north of £30m could get Albion's serious attention.
Here's how Graham Potter could fill the void next season if his two star players exit.
His departure could allow the likes of Alexis Mac Allister, Jakub Moder, Enock Mwepu, Moises Caicedo and Steven Alzate to nail down that central midfield slot.
5. Tariq Lamptey - WB
His minutes were managed last season as he returned from hamstring surgery. Next season could be a major one for the jet-heeled England under-21. Offers Albion a different dimension down the right. Photo: Mike Hewitt
6. Alexis Mac Allister - M
Looked every inch a high class Premier League player last season and delivered on a consistent basis. Could form a nice partnership with Moises Caicedo next season Photo: Stu Forster
7. Moises Caicedo - M
A brilliant start to his Albion career and he could cushion the blow of Bissouma's exit. Powerful, strong in the tackle, comfortable on the ball and drives forward. Remind you anyone? Photo: Manchester United
8. Marc Cucurella - WB
A fine introduction to last term. He is wanted by Chelsea and Man City but it would take a massive bid to prise away Albion's player of the year. Will be a key man for Potter down the left next season. Photo: Charlie Crowhurst