Patriots DE Jermaine Cunningham joins RB Brandon Bolden on the suspended list. (US Presswire)

Jermaine Cunningham’s revival of the New England Patriots’ defense, once one of the feel-good stories of the year, became tarnished Monday afternoon when the league announced that the defensive end tested positive for a banned performance-enhancing substance.

Cunningham’s four-game suspension will begin immediately, making him eligible to return for the season finale against the Miami Dolphins. The substance found in the test was not revealed.

A third-year player out of Florida, Cunningham has been one of New England’s top pass rushers, serving as the chief backup to rookie defensive end Chandler Jones, who, incidentally, is battling an ankle injury that kept him out of action during Thursday’s win over the New York Jets.

After playing just 48 total snaps last season and on the brink of being a bust, Cunningham turned it around in camp, claimed a roster spot, and has been a key contributor on defense. He has 23 tackles, 2.5 sacks and leads the team in holding penalties drawn.

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Trevor Scott, signed as a free agent during the offseason, will now likely serve as Jones’ top backup and take Cunningham’s place in sub packages.

Undrafted rookie running back Brandon Bolden is serving a four-game suspension for testing positive for a performance enhancer earlier this month.

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Nick Underhill covers the Patriots for MassLive.com. Follow him on Twitter @CBSPats or@Nick_Underhill.