The Whites lost a number key midfielders this summer, with Mousa Dembele, Clint Dempsey and Danny Murphy the headline departures. Giorgos Karagounis and Kieran Richardson have been brought in to bolster numbers but, with Mahamadou Diarra out injured for at least a month, Jol plans to bring in a defensive midfielder.
The Dutchman rejected talk it could be Owen Hargreaves or Nigel Reo-Coker, revealing instead it would be a player from abroad - and one he managed during the season the spent in charge at Hamburg. He said: "It will be a holding player because I had Chris Baird there last week and I needed him elsewhere because Senderos is still injured."
Jol continued: "Something happened to [Brede] Hangeland so I had to play Chris at the back and we struggled in midfield so I need a real number four. It's not a mystery player, the only thing is we haven't spoken to him yet.
"I don't want to mention his name because if I mention his name, maybe another club will jump on him and I don't want to take that risk. As it looks now, we tested him and he looked fine and it will be a number four who played abroad, who played for me in Hamburg."
Jol will face several other players from his Bundesliga days tomorrow when Fulham take on Manchester City. The Dutchman managed Vincent Kompany for one game at HSV before the defender left for England, while he saw Edin Dzeko's destructive goal-scoring form at Wolfsburg first hand.
"I can remember Wolfsburg being champions and it was because of him," he said. "He was the top scorer in Germany and that is not easy. But he played with quite a few good players up front if you compare Wolfsburg then with the team now. It is a big difference.
"They had Grafite, for example, who was a very good player. They had [Zvjezdan] Misimovic, they played in a certain system - the golden triangle with Dzeko.
"I think it is only a matter of time. If you play Dzeko every week then you will see he is a quality player. But of course you have got [Carlos] Tevez, [Sergio] Aguero, [Mario] Balotelli so they've got world-class players."