That, naturally, would lead to concern about Williamson's fitness, as well as potential uncertainty about how to heal the injury, but Stead is optimistic that his captain will have a simple recovery.
"It's very minor but we're hopeful he will recover quickly.
"Kane's managed his way through injuries before, he's had niggles all the time, and he seems to find a way through. The extent of this and the unknown of this were the things we were unsure about, but hopefully, he'll get through that fine.
"It's like any muscle, there's obviously irritation and a wee bit of bleeding, it's not a major injury, so we're hopeful in a short period of time, he will be back to full noise."
'Hopeful' might be the key word, and while Williamson is set to travel with the team to Christchurch for the third and final test, Stead indicated that he will only play if he's completely fit, meaning Will Young is in line to make his test debut.
"The thing for us over the next 48 to 72 hours is just to make sure he doesn't aggravate it any more.
"If he's fit, no player wants to give up their spot in the test team. But I think it's safe to say that we will probably err on the conservative side, and if there's any chance of risk then we're likely to pull him from that game."
While the World Cup in May is an obvious focus, Williamson still has the matter of the lucrative Twenty20 Indian Premier League to worry about, with the 28-year-old set to link up later this month with the Sunrisers Hyderabad.
Stead is confident that Williamson will be fit in time but stressed that New Zealand Cricket won't let the Indian franchise take any risks with their star batsman ahead of the World Cup.
"From what I've been speaking with the physio and Kane about, if things progress as we hope, then going to the IPL shouldn't be a problem for him. But he's also aware that if he's not quite 100 per cent, then we will potentially hold him back as well and make sure he is right before he goes on that plane."