Marta, named Women's Player of the Year a record six times, picked up the injury at Brazil's camp in Portugal on Sunday (AEST) and, while the CBF did not clarify how serious the injury was, coach Vadao told a Globo website she could miss their June 9 opener.
"Our worry is just about the first game," Vadao said, "and whether she has time to recover or not.
"She feels fine. We’ll wait a couple of days for the medical department to give me a more concrete appraisal."
The absence of Marta, who has scored a record 15 Women's World Cup goals, would make Brazil's life even more difficult at the June 8 to July 8 tournament in France, where they also meet the Matildas and Italy in the group phase.
The 2007 finalists come into the tournament having lost their last nine matches, their worst ever run.
