"It's complicated because the time between one match and another is very short," said Lugano, who limped off after damaging a right knee ligament during Uruguay's quarter-final win over Ghana.
Lugano's absence would be another blow to "La Celeste", who will also miss striker Luis Suarez in Tuesday's match in Cape Town. He is serving a one-match ban for handling the ball on the line against Ghana in the last moments of extra time.
Defender Jorge Fucile also misses the semi-final after picking up a second yellow card, and midfielder Nicolas Lodeiro is out after fracturing a bone in his fight foot.
Speaking at a chaotic session with several hundred journalists, Lugano said he had not given up hope and had been able to do some light practice on Sunday.
"I was lucky enough to train and run in a straight line without pain, which is good news because it's only 48 hours since I was injured," he said.
"Now we'll have to wait until the last minute. The pain is not what matters, the point is to be 100 percent ready for a match of this level and be honest with my teammates and country. Tomorrow I will evaluate if I'm OK or not."
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