3:51PM BST 20 Sep 2012
Jol revealed the potential extent of the injury Diarra suffered making his return from international exile with Mali this month.
The 31-year-old, who had not played for his country for more than a year,
damaged his left knee and was forced to miss
Jol confirmed this afternoon Diarra required some form of surgery and would miss at least another three weeks.
But if it transpires he has damaged his cruciate ligament, he could be out for up to five months.
Jol, who was expecting to learn the true extent of the damage next week, said: "There's a little piece of cartilage floating in his knee, so we have to operate that in any case, and that can be three or four weeks.
"But if there is damage to his cruciate ligament, for example, it will take a lot longer.
"It will take him three, four, five months at least."
That would be a huge blow to Fulham, whose lack of cover in midfield was demonstrated by the signing of Greece veteran Giorgos Karagounis after the transfer window closed.
That followed the summer departures of the likes of Clint Dempsey, Mousa Dembele, Danny Murphy and Dickson Etuhu.
Jol was forced to play defender Chris Baird alongside Steve Sidwell in midfield against West Brom and will do so again in Saturday's game at Wigan.
The Dutchman added: "Hopefully, we will stay fit. The advantage is that we don't have to play in Europe.
"But if Bairdy or Sidwell would get an injury then we could end up with a slight problem."
Baird's secondment has also left Jol with a defensive headache after he revealed Philippe Senderos was still not ready to step up his comeback from a broken foot by playing for the reserves.
"He needs maybe two weeks to come back and be match fit," Jol said.
"Baird, of course, plays in midfield now, so I need Philippe as soon as possible."
Jol will still be without Kieron Richardson (hip), Kerim Frei (pelvis) and Ashkan Dejagah (match fitness) this weekend, although he expected the former to resume training next week.
There was better news on the injury front for Bryan Ruiz and Mladen Petric, both of whom were declared fit to return at the DW Stadium.
And Jol also revealed Ruiz and former Wigan star Hugo Rodallega were vying for a place in his starting line-up alongside new hero Dimitar Berbatov.
"I don't tell anyone the line-up before matches but that is the big decision we have to make," he said ahead of an away game which could reveal a lot about Fulham's prospects this season.
Having won both their home matches and lost all three of their away games so far - including a Carling Cup shock at Sheffield Wednesday - the Cottagers are in danger of slipping back into their old habit of being a soft touch on their travels.
Jol cited injuries as being largely to blame and insisted his squad were capable of improving on their four away wins from last season.
He said: "We managed just four wins last year and a couple of draws. That was not good but it wasn't bad either.
"If we manage to get five or six away wins, I think we will do well."
Meanwhile, Damien Duff today retained his status as the fifth Republic of Ireland international to reach 100 caps despite being told he might not have completed a century after all.
The 33-year-old Fulham midfielder captained his country against Italy in their final group game at the Euro 2012 finals in Poznan on June 18 as he reached three figures.
However, a report claimed that the warm-up game against Hungary on June 4 in which Duff, who announced his retirement from international football last month, played, may not be recognised by Fifa because of a discrepancy with the match officials.
But after contacting both the governing body and the Hungarian Football Association today, the Football Association of Ireland has confirmed that it has discretion to award caps for the friendly and has done so.
