كتب : Sherif Tarek
The 29-year-old sustained a serious cruciate ligament injury in Dortmund's 1-1 draw with Hoffenheim in April.
Zidan underwent surgery and faced a six-month layoff.
The Port Said-born player is set to make his comeback in October as planned.
"We are working very hard," Dortmund's fitness coach Florian Wangler was quoted as saying by Bild.
"The mobility of the injured knee is back to normal. So far, everything works smoothly.
"without complications, he may get back in action late in October."
Zidan was at his best before picking up the knee injury.
He helped Egypt to a third successive African Cup of Nations title and put in impressive performances at club level throughout the season.