The Japanese international sustained the injury while on tour in South Africa and, while he has made good progress, he reports that he still feels a degree of discomfort.
"I still have a little bit of pain," said Kazu on Monday. "I can work on the bicycle, walk and jog, but when I sprint it causes some pain.
"I want to be back in the squad as soon as possible but, if I am honest, I need maybe one more week."
The injury is a setback to the midfielder who was making great strides in first team action during the pre-season campaign.
"I think, until I got the injury, I was having a good pre-season and played four or five games."
Kazuyuki Toda suspects that he is still one week away from a return to full training following his calf injury.