Phoenix coach Ricki Herbert confirmed the injury and said the club hoped Ward was back around Christmas rather than in the New Year.
"It's not the news we wanted to hear but unfortunately that (four to six weeks) is probably the time frame," Herbert said today.
"He's been playing well, that's why we signed him. He'll be immensely disappointed and I thought he had a great game on the weekend.
"Hopefully we get him back soon after Christmas."
The Phoenix are preparing to take on Gold Coast United at Skilled Park this Saturday night.