The two sides drew 0-0 in the first leg of their Europa League third round qualifying match at the Dugopolje's Stadion Hrvatski Vitezovi.
Fulham had won their previous two qualifying matches against NSI Runavik and Crusaders convincingly, but Jol felt his side did not do enough to win the game in Croatia.
"At the end of the day, we drew 0-0 away from home against a good side. I'm not happy with the result, but satisfied," said Jol.
"There certainly was not a lack of effort from my players. We didn't do enough with the ball in their half and we have to do better."
Fulham will meet RNK Split for the second leg of their match at Craven Cottage on Thursday, August 4.