It has been a transfer saga that has dragged on and on and on ... with no conclusion.
Lille are understood to value Debuchy at around eight million euros - £6.3mill.
Mike Ashley tabled an improved offer for the 27-year-old France international but his club refuse to let him go.
Lille sold midfielder Yohan Cabaye to United for a bargain £4.8million last summer, but have refused to budge on their valuation, and have now attempted to draw a line under the matter.
Seydoux: "I have decided that Mathieu Debuchy will remain at LOSC.
"The offer from Newcastle is definitely not at the value of the player. For Mathieu Debuchy to leave, it would have taken the offer to be consistent and commensurate with his replacement.
"As the conditions are not met, it is my duty to make a decision."
Current right-back Danny Simpson has only a year left on his contract and is yet to agree a new deal, but he could yet stay Tyneside.PRE-SEASON FIXTURES:
BRAGA 1 NEWCASTLE 2 (Ba, R Taylor)Harper; Simpson, Tavernier, Coloccini, R.Taylor; Sammy Ameobi (Obertan 88), Tiote (Cabaye 70), Gutierrez, Marveaux; Cisse, Ba (Vuckic 85).
OLYMPIACOS 1 NEWCASTLE 1 (S Taylor)Krul, Perch, Williamson, S.Taylor (Dummett 46), Santon, Obertan (Sammy Ameobi 72), Bigirimana, Gosling (Abeid 36), Amalfitano, Vuckic, Shola Ameobi (Cisse 72).
FENERBAHCE 1 NEWCASTLE 1 (Abeid)Elliot, Simpson (Santon 68), Tavernier, Coloccini, R Taylor, Tiote (Bigirimana 59), Gosling (Abeid 73), Obertan (Shola Ameobi 75), Marveuax (Gutierrez 59), Vuckic (Sammy Ameobi 46), Ba (Cisse 68).
MONACO 0 NEWCASTLE 1 (Ba)Harper, Santon (Ryan Taylor 57), Simpson, Williamson (Perch 46), Gutierrez, Amalfitano (Obertan 62), Abeid (Tavernier 46), Bigirimana (Tiote 62), Sammy Ameobi (Vuckic 46), Shola Ameobi (Gosling 62), Ba (Marveaux 78)
CHEMNITZER 1 NEWCASTLE 0Elliot; Tavernier (Simpson, 70), Williamson, Perch, R Taylor (Santon, 70); Obertan (Gutierrez, 77), Abeid (Bigirimana, 70), Gosling, Amalfitano; Vuckic (Shola Ameobi, 70), Sammy Ameobi (Ba, 77). Sub not used: Harper. Att: 6,700
Sat 04.08.2012 ADO Den Haag v NUFC (*an exhibition game) (5.00pm KO)
Sat 11.08.2012 Cardiff City v NUFC (at Cardiff City Stadium, Wales - 3pm KO)