He is to undergo surgery and is expected to be sidelined for about six weeks.
McCaw developed pain in his foot while doing a "yo-yo" running test in Christchurch on Monday last week.
A scan late last week confirmed he had the stress fracture in the fifth metatarsal of his right foot = the bone running down the outside of the foot to the little toe.
"The injury is obviously disappointing, but it's not likely to be one that will bother me in the long term. I'll have the operation and then get on with my rehab and look forward to turning out for the Crusaders when I'm given the all-clear by the medical staff," he said.
McCaw saw a foot and ankle surgeon in Christchurch today and has been booked for surgery to insert a small screw into the bone.
The 30-year-old McCaw had been scheduled make his return for the Crusaders on March 4 against the Waratahs after sitting out the first two rounds of the Super 15.
Metatarsal injuries have been common among footballers in the English Premier League with Manchester United striker Wayne Rooney and Liverpool midfielder Stephen Gerard both suffering an injury to the fifth metatarsal in 2004. Gerard was out for 10 weeks while Rooney spent 14 weeks on the sidelines.
Crusaders midfield back Sonny Bill Williams is also hampered by a stress fracture to his left fibula on his left leg.
