Talk just a few weeks ago revolved around a top-10 finish, but a poor run of form looks to have put paid to that.
Saturday's 4-2 home defeat to already-relegated Reading compounded a miserable run that has left the Whites just five points off the drop zone.
Jol has been frustrated by his side's recent displays and wants them to play with more passion in their remaining games against Liverpool and Swansea.
"That is disappointing," the Dutchman said. "We had 40 points at a very early stage, so that was remarkable. After that the pressure was a bit off us and now you see all these teams like Aston Villa and, before Monday, Sunderland with Paolo di Canio picking up points.
"They got spirit from that and that is what we need as well, because I feel you need to take things into your hands and you need another three points.
"The first half I was disappointed, but the second half we never gave up and were in it until it went 4-2. But it wasn't the best performance, of course. People were shouting to get Bryan Ruiz off and then he scored two goals after that.
"I was really happy because he is a good player, but it was not the best performance - not as a team, not as an individual."
Asked if his players relaxed too soon in the season, Jol said: "That is the question you ask me every week and you are right, you are entitled to get an answer. But, on the other hand, against all these teams - Newcastle away, Chelsea, Arsenal - we can't fault them for having no application.
"I think we wanted to do well, but it is more like that pressure you need to perform and get a result probably wasn't there the last three or four weeks."