Rennie will name his players next Sunday for the series, which opens in Sydney on July 7, with three Tests played in 11 days, and says there will be some changes to the 40-man training squad he named in March.
"We've got the spine of a team ... there's certainly positions that we're unsure of and the next couple of weeks are going to be important for those individuals," Rennie told Stan Sport.
After leaving out all three of the hookers he used in 2020, Rennie said the No.2 jersey still remained wide open, as did spots in the second row.