"Last time, if you look after the World Test Championship and then coming back before the IPL and the Twenty20 World Cup, it was about eight or nine weeks, so I expect somewhere in that timeframe again.
Stead said surgery is unlikely – "if we don't have to cut a tendon, our choice is not to do that" – and explained how test cricket is the troublesome format for Williamson.
"The management of Kane through the T20 games was much easier, because it's about load on the elbow, so as soon as you enter the test arena and you're looking at longer periods of time training and then batting as well, that load is what tipped him over the edge.
"In the shorter forms of the game it's more manageable, in test cricket it's tougher."
The injury has resulted in Williamson having to monitor and often reduce his training loads, something most recently seen during the T20 World Cup, in which he played every game despite minimal training.
"That's been a change of mindset to get his head around, but he's adapted really well to that," said Stead.
"There has been some time during tournaments where we've had to talk about it, get him to pull back a little bit from what he naturally wants to do. He's a prodigious trainer, he loves hitting balls, he loves being and feeling fully prepared for the matches.
"Kane's doing it tough – he loves playing for New Zealand, he hates the thought of missing any cricket, let alone test cricket."