Ifill, who has scored 28 goals for the Phoenix since his 2008 debut, injured his ankle and knee during a practice match against Central League team Petone.
He is scheduled to see a specialist, and more information was expected after scans.
The Phoenix begin their season against Sydney FC at Westpac Stadium on October 6.
Ifill was a key figure for the Phoenix last season, as they performed above expectations in making the play-offs before being beaten by Perth Glory in the minor semi-final.
But the England-born Barbados international struggled with injury, a groin problem sidelining him for much of the early season.
The setback was particularly frustrating after a serious ankle injury late in 2010 kept him on the bench at the business end of the preceding season.
