The Swiss U21 international was drafted in from Grasshoppers Zurich in August and has flourished since making his debut at Everton in October.
A run of fine displays was capped by the 18-year-old's first goal on Saturday - drilling home a close-range volley in the 5-2 win against Everton.
"Reto is a young player and one for the future, I've said that before," said Head Coach Martin.
"He's played many games, had a little injury at Blackburn but after that he played again, never complained and is doing well.
"We couldn't have hoped that he'd have played so early and so well.
"He's playing like a 22, 23 year old when in fact he's only 18 and that makes him a terrific asset for Tottenham Hotspur."
The emergence of Reto Ziegler is a real bonus for Martin Jol in the youngster's first season in England.