Petric has been amongst the goals in preseason action so far.
"Mladen Petric can make a difference and he certainly showed that with the first goal on Saturday. Of course I know him from Hamburg but hopefully he will do it in the future as well," Jol told fulhamfc.com.
"I'm happy with how pre-season is going. In hindsight you can say that it has paid off and to go to Germany was good."