A host of Premier League sides, including West Brom, have been sniffing around the 21-year-old, who has smashed in 28 goals this season.
But Wilson has warned any potential suitors that they are willing to fend off any interest for the talented striker.
"Every club has the dilemma of whether they can keep hold of their best players," the Robins boss said.
"But it's a lot more positive for us as we know that Simon is very happy at the club.
"But he's not for sale and we won't be inviting offers. We'll sit back and see what happens.
"That's not to say we will stand in the lad's way if he has ambitions of playing at a higher level, as at the moment we're not able to offer that, but we have a target and a plan going forward and we want Simon to be a part of that."
Swindon are believed to be holding out for a fee in excess of £1million for their young marksman.
And Wilson added: "If something concrete does come about and we are happy that the offer to the club and the player is acceptable, then we will all sit down together and decide what the best option is."
Cox joined the Robins on a permanent deal in January 2008 and has hit a total of 34 goals in 65 games for the club.