The 31-year-old, who has only recently returned to training, could be out until next year, according to Craven Cottage boss Martin Jol
The 31-year-old had only recently returned to training but after suffering from further complications, the former Wales international is set for a lengthy spell on the treatment table.
"Simon has a pretty tough injury," Jol told reporters.
"He will be out for the next couple of months. It is a technical thing. It could be four to five months."
The Welshman's injury plagued career will be a familiar headache for Jol, who previously worked with the former Peterborough winger at Tottenham, before sanctioning his switch to Everton.