The number eight was ruled out of the British & Irish Lions tour to New Zealand due to shoulder surgery but has already returned to training and had hoped to be ready for the opening weekend clash at home to Northampton.
Sarries are currently managing a number of their stars, with Owen Farrell, Maro Itoje, Mako Vunipola, Jamie George and new signing Liam Williams all expected to sit out the first couple of weeks of the season following their exploits with the Lions.
McCall has revealed that Vunipola is in a similar situation and that the club are holding him back for his own good.
He told the Express: "Billy is due back some time in October but in true Billy style, he will make it back before that. He is chomping at the bit and the medics are taking care of him, but it won't be long."