Cook, who fast-tracked Gelhardt into his senior squad at the start of this season, is calm amid rumours of Liverpool and Wolves interest.
He told the Wigan Evening Post: “If you look around all football clubs these days, players move on, they come and go.
“If Joffy (Gelhardt) keeps progressing at the rate he has been...will he be at Wigan Athletic for the next 10 years? I very much doubt he will!
“This is the game today. But I genuinely know, from the chairman all the way down, we are not looking to sell players like that.
“We want to grow this club, and enhance it to its full potential. What is that full potential? Well that's what we're trying to find out.
“When teams are doing well, normally their players are coveted by other club."