Scans on Monday confirmed the 22-year-old hyperextended his knee in the third term of his side's NAB Cup win over the Sydney Swans on Sunday.
"Couple of weeks, that's max I think," Stanley told reporters as he left the scanning centre.
"(I'm) feeling pretty good, I just had the scans and saw the doc, so all feeling pretty good, all pretty positive."
Asked about the prospects of playing round one, Stanley conceded he wasn't sure.
"To be honest I don't know, I've got to speak to the docs again tomorrow, and yeah we'll find out from there," he said.
In a statement later on Monday the club said Stanley had received "no structural damage, but some bone bruising."
Matt Thompson is a reporter for AFL Media. Follow him on Twitter @MattThompsonAFL
