some herbal teas do have ingredients that can affect blood clotting, although mildly and increase your risk of bleeding. Excessive drinking would be worse. To be safe refrain from 10 days before the surgery.
Dear Forte, Green tea contains a number of agents that can act to "thin" your blood and impact the ability of your blood to clot. The effect of these agents varies greatly from person to person but rather than find out if you are someone who is very sensitive to the blood thinning effects of green tea, it is probably better to stop drinking green tea 2-3 weeks before your surgery. Better safe than sorry. Hope this helps.