The 18-year-old, who made 25 appearances last term, suffered the knock while on international duty with Turkey and has yet to feature for the Cottagers this season.
Frei revealed that he has been training for just under a week but has begun to work on his match fitness ahead of his return to first-team action.
"Last week on Thursday I started training again. We've been making sure that I didn’t come back too fast in case the injury came back," the youngster told Fulham's official website.
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"I missed playing football very much, I missed having the ball at my feet and things like that but I'm very happy to be back and I'm looking forward to playing my part in the season ahead."
Alexander Kacaniklic has made an encouraging start on Fulham's left flank this season and Frei sees the competition on the wings at Craven Cottage as a positive incentive to get back into Jol's plans.
"It’s always good to have competition for places. It makes you work harder as you always want to be the best," said the Swiss midfielder.
"But just one person can play in each position so you obviously have to work hard and try your best and never give up at all."