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.
1. Rob Sanchez - GK
The Spain international is Potter's trusted No 1 although he will face more competition next season from Kjell Scherpen. Photo: Bryn Lennon
2. Joel Veltman - D
Albion's Mr Reliable last season. Rarely puts a foot wrong, strong in the tackle and good in one v one situations - which is key in a Potter team Photo: Steve Bardens
3. Lewis Dunk - D
The skipper is back to his best after a knee injury and remains the rock Potter's team is built on Photo: Naomi Baker
4. Adam Webster - D
A huge season awaits after last terms' injury issues. His ability to bring the ball out from the back is a key asset. He will hope for a run of games and get himself back in the England conversation - he is good enough! Photo: Steve Bardens