The Mexican arrived at the Vicente Calderon from Club America this summer, but has thus far struggled to produce his best form for the club.
"I see Raul working very hard. He trains every day with enthusiasm and with hopes of improving. I have no doubt that he's going to contribute some important things this season," Simeone told reporters.
"It's not easy to come from Mexico into Europe and settle straight away. We are confident in his abilities and I'm convinced he will come good for us."
Jimenez, 23, has made three league appearances for Atletico this season.