A large number of Football Ferns players have written formal complaints against coach Andreas Heraf.

New Zealand Football confirmed the news in a statement, saying that they are reviewing the complaints levelled against Heraf, and that developments will be updated tomorrow.

After Heraf criticised his players following their 3-1 loss to Japan in Wellington earlier this month, it is understood that at least 10 players have penned letters about the conduct of the Austrian.

Former Football Ferns Abby Erceg and Katie Duncan have publicly criticised Heraf's conduct in charge of the side, although the coach has received public backing from New Zealand Football CEO Andy Martin.

"He was brought in as the technical director with a clear purpose," Martin told 1 NEWS last week.

"We've got this jigsaw around the talent space that has not been cracked for a long time. Andreas was the best candidate in that area. He'll be judged on that technical plan."