"During Sean's run today with our medical staff, he suffered an injury," Falcons head coach Mike Smith said. "We sent Sean to the doctor for some additional testing and evaluation and unfortunately the results showed that he ruptured his Achilles tendon.
"Sean had been working extremely hard to get back on the field, but regrettably he will miss the entire 2014 season. He will have a procedure done in the near future and we expect him to make a full recovery."
The emotional leader of the Falcons' defense, Weatherspoon was limited to seven games last season. He missed the first seven games with a foot injury, and then the final two weeks with a right knee injury that he has been rehabbing this offseason.
With Weatherspoon playing less than half the season, the Falcons' run defense allowed an average of 4.8 yards per carry, second-highest in the NFL, as the team was forced to rely on undrafted rookies Paul Worrilow and Joplo Bartu.
Bartu will be the leading candidate to replace Weatherspoon again this season. Undrafted out of Texas State in 2013, he earned snaps in the team's nickel defense with his cover skills during training camp. With Weatherspoon opening the season on injured reserve, Bartu continued to see increased playing time and went on to finish his rookie season with 85 tackles and 3.5 sacks.
Another potential option is Price Shembo, a fourth-round pick out of Notre Dame who could be a good fit at the left outside linebacker spot. He isn't a dynamic athlete and was the 19th-ranked outside linebacker in the 2014 class by NFLDraftScout.com, but he did also play end for the Irish, can rush the passer and posted a good 4.67-second 40-yard dash time at the Scouting Combine.
Weatherspoon, 26, is entering the final year of his contract.