The Falcons on Friday said an MRI exam revealed a "minor" injury that will require Neal to undergo arthroscopic knee surgery on Monday. The team listed the timetable for his recovery as three to four weeks.
Neal, the No. 17 overall pick in this year's draft, was expected to start for Atlanta in the season opener against Tampa Bay on Sept. 11.
Falcons coach Dan Quinn told reporters that the "worst-case" scenario for Neal, 21, would be to miss the first three games of the regular season.
"From all of us who know Keanu, you know he's going to put a thousand percent into all the rehab to get ready," Quinn said. "We know kind of what he stands for and the toughness, so I'd expect the shorter-term. He's kind of just built that way."
The 6-foot, 211-pound Neal played three seasons at the University of Florida. He had three interceptions in 2014 and ranked 10th in the SEC with 51 solo tackles in 2015.