Blackmon reportedly violated the NFL's Policy and Program for Substances of Abuse, according to NFL.com's Ian Rapoport. The exact nature of Blackmon's violation is currently unknown.
Blackmon will be eligible to return to Jacksonville's roster on Monday, Sept. 30, after the Jaguars host the Indianapolis Colts in Week 4. Blackmon is eligible to participate in training camp and Jacksonville's four preseason contests.
As a rookie in 2012, Blackmon caught 64 passes for 865 yards and five touchdowns. Jaguars quarterbacks targeted the former Oklahoma State wideout 133 times -- the most of any Jaguars wide receiver in 2012.
Losing Blackmon for a quarter of the season is a blow to Jacksonville's passing game. Blackmon was slated to start opposite Cecil Shorts at wide receiver for the Jaguars in 2013. With Blackmon suspended for the first four games of the season, Mohamed Massaquoi will likely start opposite Shorts in Week 1. Jacksonville signed Massaquoi to a two-year contract this offseason, after he caught 17 passes in nine games for the Browns in 2012.
Blackmon was previously arrested twice for driving under the influence -- once while a member of the Oklahoma State Cowboys in 2010, and once in 2012, just over a month after he was drafted by the Jaguars.