Coach Mike Smith said Tuesday tests revealed Tatupu will require season-ending surgery.
A team source told ESPN NFL Insider Adam Schefter that Tatupu suffered a torn pectoral muscle.
The Falcons report for training camp on Wednesday. Akeem Dent, a third-round pick from Georgia in 2011, and veteran Mike Peterson, who was re-signed on Monday, will compete for the starting job at middle linebacker when camp opens Thursday.
Curtis Lofton, the team's leading tackler the past three years, signed with New Orleans.
Tatupu signed with the Falcons in March to a two-year deal with a maximum value of $5.75 million, ESPN's Josina Anderson reported, after missing the entire 2011 campaign and being cut by the Seattle Seahawks prior to the start of the season.
Only $600,000 of the deal was guaranteed.
The 29-year-old played a key role in Seattle's trip to the Super Bowl during his rookie season of 2005, but his career has been slowed by a slew of injuries, including a previous pectoral muscle tear that cost him most of the 2009 season.
A three-time Pro Bowler, Tatupu last played a full 16-game slate in 2010 but recorded just 88 tackles -- his fewest in a full season. At the conclusion of the 2010 season, he had surgery on both knees.
Information from The Associated Press was used in this report.