According to The Daily Mail, Sunderland have made an offer of £250,000 to Wigan for Grigg.
Cook told Wigan Today regarding Grigg: “As far as I’m concerned, as manager of Wigan Athletic...Will Grigg is, not our main striker, because that would be disrespectful to the others.
“But he is very much a focal point of what we’re trying to do, within the system of how we want to play.”
“I would like to think that I speak to my players a lot - and me and Will have had conversations,” added Cook.
“It’s hard in football, because for a manager to say ‘nobody is for sale’ would just be wrong. But are we looking to sell players? Not a chance. Why would we?”
Grigg is not guaranteed a place in the Wigan starting lineup at the moment, and his record in the Championship is not especially great.
However, with the Latics in danger of getting relegated to League One at the end of the season, the Championship club will need the 27-year-old Northern Ireland international striker in the coming months.
It does not make much sense for Wigan manager Cook to let a striker leave in the middle of the season.
The striker has made 10 starts and six substitute appearances in the Championship for Wigan so far this season, scoring four goals and providing one assist in the process, according to WhoScored.
Good signing for Sunderland
Grigg, though, will be a very good signing for Sunderland in the January transfer window.
If the Black Cats are able to secure the services of the striker this month, then they will give themselves a massive chance of finishing in the top two of the League One table this season.