Sean Davis will be out of action for up to six weeks after a scan on his right knee revealed the full extent of his injury.
The midfielder damaged the medial area of his knee in last week's pre-season victory over Austrian side ASK Voitsberg.
The setback means Davis is likely to miss the first two games of the season against Middlesbrough and Everton.
Speaking to Fulham Today, Club Physio Jason Palmer explained in further detail.
"Sean has a Grade Two injury to the medial ligament of his right knee. He's just had a scan which confirmed our diagnosis.
"He's going to have a couple of day's rest before joining us in Scotland where we will continue with further treatment. If all goes well, we're looking at a recovery time of five to six weeks."
Now that the full extent on the injury is known, plans have been formulated for Davis' rehabilitation.
"For the first couple of weeks he'll be in a brace which will control his knee's range of motion," said Palmer.
"We'll then start him on some strengthening work just to make sure there isn't much muscle wastage. Within a few weeks we'll have him doing some heavy strengthening and balance work. He's now almost at the point where he can take pressure on his leg but you've got to be careful in the early stages of recovery not to put too much weight on the area."