Speaking about the injury, the Fulham boss told reporters: "Hopefully it is not a long one."
Wayne Rooney scored the only goal of the game, with a late strike, to increase United' lead at the top of the table to 10 points.
Despite the defeat, Jol was full of praise for his side, who created a host of chances in a tight game in west London.
The former Tottenham manager added: "We did well in midfield and at the back, it was one of our better performances this season.
"But they are capable of creating something out of nothing, as Rooney did. Now, I think they will win it."The contest was briefly paused before half-time as Craven Cottage was plunged into darkness following a floodlight failure, leaving the 56-year-old Dutchman concerned that his side would lose their focus.
He added: "We did well to get the lights on again normally it takes a long time.
"I feared when we came back our concentration was down and we would end up conceding a goal but it wasn't a problem."