Mohamed Zidan was not able to train with Borussia Dortmund on Tuesday due to a foot problem he suffered in training. "I have to rest now, it remains to be seen when I would return to full training," the Egyptian was quoted as saying by Bild. Zidan is already facing competition with the fit-again Alexander Frei, who made his return from a knee injury sustained in EURO 2008. Switzerland captain Frei is tipped to join Nelson Valdez upfront when Dortmund take on Schalke on Saturday.