It has been confirmed the French prospect will remain at the disposal of incoming coach Rene Girard for next season
The 20-year-old is regarded as one of the country's brightest talents, thus prompting les Dogues to snap him up from Bastia in January, though leaving him there on loan till the end of 2012-13.
But the France youth international is now believed to be disappointed with Rudi Garcia's departure from Stade Metropole, allowing league runners' up Marseille into the picture with a reported offer to triple his salary.
However, Seydoux has moved quickly to stamp out the rumour, telling France Football: "There is no case with Thauvin.
"When I say no, that's it. I have said this about a lot of players and I believe they have all stayed."
The youngster mustered 10 goals in 32 league appearances under Frederic Hantz last term, allowing Bastia to achieve a respectable 12th position and comfortable survival.
For his efforts, Thauvin was named Ligue 1's Young Player of the Season.