The 29-year-old is keen to join Liverpool but the Reds have yet to lodge an official bid for the USA international.
"Mentally Clint wants to move, he doesn't want to stay here," said Jol. "His head was turned and that was the problem.
"It's a problem and a situation you don't want. It's not something you can talk to a player about every day because he doesn't want to.
"I don't know if he'll remain a Fulham player. I'd love to keep him, but I'm not sure."
Jol added that he will have no problem with Dempsey should the former New England Revolution star remain at Craven Cottage and continue to be professional.
"Hopefully if he stays, then in the next couple of weeks he will change his thoughts about us," said the Dutchman.
"With me there's no problem and I don't think there's a problem within the team over him."
Fulham made a formal complaint to the Premier League on Thursday regarding comments made by Liverpool officials on Dempsey.