The 22-year-old has made more than 50 appearances in all competitions for the Stade Geoffroy-Guichard outfit since arriving from Troyes in 2007, and earned caps at both French U19 and U21 level, making 24 outings for the latter.
Arsenal, Tottenham Hotspur and Everton have all been linked with moves for the midfielder during the close-season.
And Comolli, a former Gunners scout and Spurs director of football, has revealed that although St Etienne are loathed to let go of their prize asset, they may have no choice should a big club make a move for his services.
"He is not for sale. We are not looking for an offer," he said.
"However, it would be difficult to prevent him from leaving if a top 10 European side came in for him."
NEWS: Matuidi reaffirms desire to move on
NEWS: Toffees to trump Arsenal for Matuidi
NEWS: Matuidi move to England edges nearer
NEWS: Comolli to assist Arsenal move for Matuidi?
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