Goal ace Dempsey, 29, moved to Spurs for £6million on the final day of last August's transfer window.
Jol said: "We miss his goals from midfield. He was not the one who ought to have supplied us with all the goals but he did over the last two or three years.
"Can you imagine the scenario if Clint hadn't been here over those years?
"If he had stayed I think yes we would have been in the top 10. Now the aim is to stay in the Premier League."