According to the A.J. Brown page, he suffered a high ankle sprain in Week 1 and reports indicate he will be sidelined for roughly six weeks. That puts his return around mid-to-late October, though the page notes his return timeline is uncertain and the original report said he should be back "within a month or two."
On top of that, he also has chronic knee management issues to monitor long-term, but the high ankle sprain is the immediate concern.