The South African-born left-armer has been the best bowler in the Plunket Shield for the past few seasons and, with seven for 46 against Wellington and the University Oval on Monday, his eventual selection would appear inevitable.
The 26-year-old arrived in New Zealand to play for Otago in October 2008, with the understanding he would qualify to play for his adopted country in three years. He actually had to wait four years.
New Zealand Cricket's national selection manager, Kim Littlejohn, said the ICC rules were clear.
"The ICC rules state you need to complete four consecutive years where you are in the country for 183 days," Littlejohn said.
"I think what everyone has got a bit confused about is they think it is four consecutive cricket seasons."
While Wagner has played for Otago for four seasons, he will not have lived in New Zealand for four years until October this year. Complicating matters, Wagner left the country briefly to attend a wedding and also to play for Otago at the Champions League in India.
Littlejohn said New Zealand Cricket was still working with the ICC to get a definitive date for Wagner's eligibility.
"We expect the ruling sooner, rather than later, but the ICC is one of these big organisations which takes forever. We are hoping to have something back in April, so I can give Neil an answer one way or the other so he knows exactly where he stands.
"We want to know where he stands, as well, because we have a substantial schedule of cricket coming up over our winter and for the rest of this year."
New Zealand has tours to the West Indies, Sri Lanka, India and South Africa coming up and a home series against England early next year.
Littlejohn said the ICC had strict rules around eligibility which made it hard for cricketers to relocate to a new country.
"It does not allow for free movement for people wanting to change countries. I can understand the ICC wanting to try and stop people changing on a yearly basis, but it does make it hard for people when they have to sit out for four years before they can represent another country."
