Queens Park Rangers submitted an offer for the striker yesterday, believed to be in the region of £2m.
However, Fulham rejected that bid and Jol has revealed that the club would only sell the 30-year-old for the right price.
"What's the point for us - for Fulham, for my club - to sell a player for that sort of money?" Jol said. "To get somebody will cost a lot more money so for me there is no problem.
"He is still under contract so we have to wait and see.
"If somebody wants him they have to pay a good transfer fee so we can buy another good player."
Blackburn Rovers are also reportedly interested in Johnson's services.