League sources told NFL Media and SiriusXM NFL Radio on Thursday that Flacco had the neck procedure in early April. According to NFL Media, he underwent a 45-minute disc repair and won't be cleared to return until late August or mid-September.
Flacco, 35, landed on injured reserve after only eight games last season because of the neck injury. The Broncos placed him on IR in November and eventually released the former Baltimore Ravens signal-caller this off-season.
In eight games with the Broncos last year, Flacco threw for 1,822 yards with six touchdowns and five interceptions. After Flacco's injury, Denver turned to rookie gunslinger Drew Lock, who finished with 1,020 passing yards, seven touchdowns and three picks in five starts.
The Ravens selected Flacco in the first round of the 2008 NFL Draft out of Delaware. Flacco, who was named Super Bowl XLVII MVP, has recorded 40,067 passing yards, 218 touchdowns and 141 interceptions in his NFL career.