It emerged on Thursday that the Magpies had tabled an improved offer for the 27-year-old France international after a pursuit lasting months.
However, Lille, who sold midfielder Yohan Cabaye to the Tyneside club for a bargain £4.8million last summer, have refused to budge on their valuation, and Seydoux told L'Equipe: "I have decided that Mathieu Debuchy will remain at LOSC."
He added: "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."