MD Paul Aldridge confirms:
"There is an agreement in principle but as things are at this moment the transfer is not quite completed."
Sebastien is a 21 year old midfielder who can play on the left or the right.
The club are awaiting international clearance from the French FA, but in any event he will not be eligible to play at the weekend.
Meanwhile Celtic keeper Magnus Hedman, about whom West Ham made an enquiry recently, is joining Ancona on loan.