Justin Blackmon suspended four games by NFL

Jacksonville Jaguars wide receiver Justin Blackmon's up-and-down rookie season ended on a positive note with a strong statistical finish. His second season is starting off on a huge down note.

The NFL announced Tuesday that Blackmon has been suspended without pay for the Jaguars' first four games of the 2013 regular season for violating the NFL Policy and Program for Substances of Abuse.

Blackmon will be eligible to return to the Jaguars' active roster Sept. 30, following the team's Week 4 game against the Indianapolis Colts.

"I've made a mistake and I have no excuse," Blackmon said in a statement released by the Jaguars. "I am truly sorry and disappointed in myself for putting the Jaguars in this situation, and I look forward to putting this behind me and maturing and growing as a person."

The news is a significant blow to a moribund Jaguars offense that is trying to find new life under coach Gus Bradley. Without Blackmon in the mix, the team's top receivers are Cecil Shorts, Mohamed Massaquoi, Jordan Shipley and rookie Ace Sanders. Perhaps the Jaguars will use fifth-round draft pick Denard Robinson at receiver as well. Quarterbacks Blaine Gabbert and Chad Henne aren't exactly playing with a stacked deck.

For Blackmon, this is a terrible first impression with the new Jaguars regime, including general manager Dave Caldwell. Citing a source who saw the contract, NFL.com's Ian Rapoport reported during Tuesday's "NFL Total Access" that the guarantees in Blackmon's deal have become "null and void" as a result of the violation.

It's unclear how Blackmon violated the policy, which remains confidential. It takes repeat offenses to incur a suspension.

"It's very disappointing," Caldwell told reporters on Tuesday, according to the Florida Times-Union. "We understand this isn't all going to be on an upward trend and we're going to have setbacks. To be honest, things like this are frustrating because it's an avoidable situation."

"When we first got here, we talked to Justin and we've had numerous talks with him, even as of late," Caldwell said. "He realizes he's at a crossroads not only in his career, but his life."

UPDATE: The Jaguars were aware of Blackmon's impending suspension "long before" the 2013 NFL Draft, a source with knowledge of the team's thinking told NFL.com's Ian Rapoport on Wednesday. Jaguars general manager Dave Caldwell and the new coaching staff haven't encountered any behavioral problems with Blackmon, the source said.

Follow Gregg Rosenthal on Twitter @greggrosenthal.