Even with an operation, which is likely to take place in the next two days, Hernandez, who is looking to book a place in the Costa Rica team for the World Cup, will be out of action for more than a month, which means he will miss friendly games against Chile and Korea at the end of January.
Phoenix coach Ernie Merrick said the injury came out of an innocuous challenge during last Friday's 1-0 win over Melbourne Heart.
"Carlos fell on his wrist and twisted it at the same time,'' Merrick said.
"He told us it was aching that night so we had it strapped.
"It seemed fine, but after training the next day the ache was back so we sent him for an X-ray. That revealed a fractured scaphoid bone that needed operating on as soon as possible.
"He can't play or train till that is done.''
Wellington meet the Western Sydney Wanderers across the Tasman tomorrow night and Merrick said the injury meant changing a combination that had won the last two games but remained confident he could call on someone to do Hernandez's job in the midfield.
"I'll make a decision about who will do that job on match day,'' he said. "Make no mistake we are going for a win; nothing less.
"We have drawn twice with last year's premiers, and have some momentum built up after winning our last two games.''
On a positive note Stein Huysegems, who has had a hamstring strain, came through the final training session without a problem today and Louis Fenton also pulled up well.
While Huysegems, scorer of the winning goals in the last two games, will definitely start, Merrick will make a decision on Fenton tomorrow morning.
