The 35-year-old Frenchman has featured in every minute of Spurs' Premier campaign so far, as the North London club have taken two points from their opening three games.
"We have to work again for the next game, to improve again. We have to fight," William told the club's official website.
"In the Premier League now, when you saw how Norwich played and I would say they played well, they were compact, maybe we didn't play quick.
"So they had time to come back and be ready for the counter-attack. We have to improve on that."
Next up for Spurs is a trip to Reading on Sunday.