The 29-year-old American's current deal expires in the summer of 2013, however Jol has hinted that he may leave before then if no agreement is made.
"We're talking to him and hopefully we'll get it right," the Dutchman told The Sun.
"If you've a year to go, it's hard to keep someone even if you want to.
"You can keep him on that deal until it finishes but of course that'll be a difficult situation for everyone."
Dempsey, who has scored 22 goals for the Cottagers this season, had been linked with a £7m move to Roma.