The Costa Rica international moved to Craven Cottage from FC Twente in a deal worth a reported £10.6million on transfer deadline day. Ruiz cut a frustrated figure during his first few months in west London as he struggled to reach full fitness, although he is now beginning to show his true worth.
The 26-year-old scored an exquisite scooped effort in the 2-0 defeat of Bolton at the weekend and Jol believes there is more to come. Ahead of Wednesday night's match with Manchester United, the Dutchman said: "Ruiz will be an important player for us.
"If you talk about the season after next season it would be a bit late. Hopefully he can show his productivity in the next couple of months.
"I think he's got the same [skill] as [Mousa] Dembele, but I won't say that he's a crowd pleaser because I don't think that they care about pleasing the crowd.
"I think he will please himself if he plays well and he knows that he can play well."